The Nitrogen Cycle for Everyone

nitrogen cycle in a fish tank

Creative Commons License courtesy of KasiaJB

If this blog had a second title, it would be “How to Not Kill Your Fish.” Please read on.

Establishing the Nitrogen Cycle in your new aquarium is the single most important step toward successful fish keeping, although you may not hear about it in the pet shop. Why is the Nitrogen Cycle so important? Because most living things produce toxic ammonia when they eat, grow, breathe and drink. People can shower it away or flush it away, but an aquarium fish has to live in a closed environment. What goes in stays in and will poison the fish if it’s not removed or converted to something harmless. That’s where the nitrogen cycle comes in.

We call it the Nitrogen Cycle because toxins like ammonia (NH3), nitrite (NO2) and nitrate (NO3) are nitrogen compounds, and that’s all the chemistry words we need for now. Another important word is itty bitty bugs, which some people call bacteria. Little bugs are everywhere, and some of them are very good for your aquarium. In fact, different kinds of bugs eat the toxic ammonia, nitrites and nitrates that get put into the aquarium by the fish, uneaten food, dead plants and the occasional curious cat.

When your aquarium has enough good bugs, they will convert all the toxins into plant food. Almost like magic, the good bugs get into your aquarium. All you need to do is feed them and give them a few weeks to grow BEFORE you add fish. The good little microscopic bugs will eat flake food or even small hunks of raw shrimp or fish. They live mostly in the substrate (gravel or sand) and filter elements, so if you have an old filter or gravel from an established aquarium, try to use some in your new aquarium. You may be able to speed the Nitrogen Cycle up by adding one of the new products that contain live bacteria. However, the process will still take some time; it is not complete until ammonia and nitrite stay at zero measured concentration, and nitrate is below 40 ppm.

The main task for the aquarist while all those good bugs are growing is to wait a few weeks. The wait gives you an opportunity to get a test kit to measure at least ammonia and nitrite, and do some research on the species of fish you want to keep. They all need different things. You can also add plants and operate the light and filter, but NO FISH YET.

After all that difficult waiting, you can test the water for ammonia, nitrite and nitrate. When measurements stay at the above limits for a couple of days, the nitrogen cycle is working and the aquarium is ready for fish. The colonies of bacteria will grow just enough to handle the toxins, but they can handle only so much, so don’t overwhelm them with too many fish or too much food. If everything works like it should, you’ll have a well balanced aquarium. To maintain that balance, change 25 or 30 percent or so of the water every week, and don’t forget to use a good water conditioner.

Some tap water conditioners like Prime and Amquel will neutralize toxic nitrogen compounds for about 48 hours while still making it available to feed bacteria growth. Some of these tap water conditioners will help protect the fish if you already added them before growing a nitrogen cycle. Be aware that some tap water disinfectants and conditioners can mess up test readings, so sample and test the water just before a partial water change.

Here are some links to related information:

So... what do you think? Please leave me a comment.

Johnarthur is a veteran at My Aquarium Club.


  • johnarthur: The above is an over simplified version of the nitrogen cycle, but it puts down the basics. I hope and expect that forum members will relate some of their own experiences with the nitrogen cycle and will add comments.
  • johnarthur: Help. How can i enlarge the graphic that Crissy did????
  • KasiaJB: better ask Crissy :-) really :-) so she can send you/post a higher resolution pic
  • KasiaJB: John I just checked and Crissy’s pic is big (over 31×40cm) when I put it in to my blog but no text just pic it looks big on the preview. What picture have you used - I mean from where you saved or dragged? Do it from original pic Crissy posted and it should be big. If you ‘d like I can post it to test on my blog of it helps at all - unsure.
  • johnarthur: Any help is welcome. That’s a perfect graphic, and i’m an imperfect computer operator.
  • KasiaJB: I tried with your text and on preview it looks okay big size picture but if I post it I highjack your blog post :-( try dragging crissy’s original picture on you desktop then go to your blog and upload it to you blog from desktop and drag again to your post. I can try it for real and later delete?
  • Crissy: [IMG][/IMG]
  • Crissy: I think the reason why its coming out like that is because its so **** big.
  • Crissy: How about this one Kasia? I resized it smaller so it wont be squished.
  • KasiaJB: I never had a size issue with this diagram could see it big, could link, everything. This new link also works for me. I think resizing to smaller for Johns purpose can be done after downloading/dragging in photoshop. although maybe John doesnt have a photoshop or any graphic program? Lets see what he says. I think the diagram looks perfect on photoalbum not too big imo and on the link as well! Such a good job you have done Crissy!
  • Crissy: Thank you, but I’d wish there would be a way to fit it perfectly (view wise) as an addition to the blog itself D:
  • KasiaJB: well as I said I have it now in my blog saved johns text plus what looks like big size of your diagram in preview it looks good.
  • Ebrahim: john i think u should have stressed a bit more on the need for patience on the aquarists side.but overall a very good and well written article
  • johnarthur: Please keep adding comments. They should be very helpful to new aquarists.
  • Michelle_M: Is it better to use live plants or plastic plants when first starting out? Do the plants play a large part in the nitrogen cycle? I have now cleaned and put the chemicals into my son’s tank. Now we wait. The waiting part is hard, but it is for a good reason.
  • mjrkiller308: i love my live plants but for a beginner go with the fake plants they are just as hard if not harder to keep healthy and growing also can be expensive too. they do play a big part in the cycle process they say to snap off a part of ur plant and put it in the cycelin tank to help with the bacteria part of the cycle. and yes the waitingpart is very improtant but it will be worth it i promise. gl mgf
  • MrBreeze: Wow. Wish I had been more patient with this particular topic. I bought a 55 gal used. I got set up, added well rinsed gravel and ran lights, filter and air for about 48 hours. On the third day, after work, I took a water sample to the local petsmart. The young guy working there was very helpful in testing my water in a professional manner. I’m confident in the results....but I’m less than confident in the professionalism of the advice I was given. I specifically asked "Ok, so my water tests good in all areas and I’ve maintained 81 degrees for over a day. Am I ready for fish?" He was happy to sell me fish...but as I’ve read here, that’s likely to not be the desired outcome for this scenario. Today is 14 days since fish were introduced. There have been no visible changes to the fish, except they’ve grown and become comfortable with me, even curious of me. Today I picked up a test kit and found my nitrAte @ about 15 ppm and 0.5 ppm nitrIte. Fortunately I was already planning a 25% change but opted for 40% based on the results of testing. I managed to maintain +/- 2 degrees during the process and it has stabilized at 80 now...right where its been for 14 days. My fish already seem more energetic and lively. I’ll test daily for a while and plan a 25% change sunday evening. Live and learn I guess...hope they haven’t been miserable due to my impatience/ignorance. Any thoughts (and I don’t mean thoughts about my ignorance either...haha).
  • MrBreeze: btw...the chart was highly entertaining! The size was ok....for Imax! Just kiddin of course.
  • johnarthur: In response to the question about plants, live ones help water quality by producing oxygen, and some like water sprite and hornwort metabolise toxins. Of course, they also bring snail eggs into the aquarium, and dead plants can make a mess. On balance, I think undemanding plants are worth the effort.
  • Ahsima Patel: Good explanation. Thanks. Why do we need motor for the fish tank?
  • johnarthur: By "motor" I assume you mean pump or filter. If the aquarium had the right plants and very few fish, it would not need filtration. However, most of us want lots of fish and tend to feed them too much. Filtering systems more or less compensate for those things, and regular partial water changes simulate the constant flow-through that natural freshwater systems have.
  • cheekers: this whole time ive been changing alll the water,,,i only needed to change half of the water,,,,i have a betta no wonder he only stays at the top...
  • johnarthur: A smaller (25 percent) partial water change is less likely than a 50 percent change to cause rapid changes in water parameters. If the aquarium is small, the larger water change may be necessary. Be sure the temperature of the replacement water is about the same as the aquarium temperature.
  • Gail: He is about 2 years old a little over,he is laying on his side sometimes right and sometimes left..he tries to sit up but has a hard time.What is wrong?
  • johnarthur: Poor water quality will weaken a fish’s immune system and invite diseases and parasites to invade. Make sure water parameters are appropriate, and verify zero ammonia and nitrite. After any water quality issues are solved, go to the TOP ARTICLES list at the upper left of the page and find the chart about fish maladies and treatments.
  • zoeythe mermaid: that would explain so much i still have questions
  • zoeythe mermaid: john can you email me plz
  • Prabhu: Great photo sir i like it
  • meetamol: very good doc.
  • Sonia: Good example john
  • Calabaloza: John, mind if I steal your picture and send it to my friend?
  • Micky: thank you so very much for all your advice ...I will copy it and keep it very handy ...cause I did everything wrong and all my fishes died and I am so very upset it’s not even funny ...if I can take couple minutes of your time I would tell you that I kept 2 gold fishes 1 placo and 2 cat fises and 4 snails in a 10 gallons fresh water tank for 7 months and they all were doing fine ....the fact that they were so big I went to put them in my son’s pound and thet disapear never to see them again ...don’t need to tell you my guilt..yet it was same water as it came from underground ....since I had my water analyse because I cleaned up the tank and I had to add up bacteries wich I did but nobody told me not to buy and add other fishes so I bought 3 hatchets and 5 little fihes and they all died ..and I cried so I bought a oranda and 2 catfishes and a sucker and they all died and I am ready to thro my tank on the trash because I think it’s cursed ...the only thing I have are my 4 snails ....any advice would be sooooooooooo appreciat ...thank you very much to read me all the way ...have the greatest day
  • johnarthur: The beneficial bacteria associated with the nitrogen cycle live mostly in the substrate and filter elements, not the water column. Using water from an established aquarium will not transfer the nitrogen cycle. Only the gravel and filter elements will do that.
    Goldfish are a cool water species and should not be kept with tropical fish.
  • Tricia: Thank you very much for your time and informative answers! Much appreciated!
  • Izumi: Thank you so much! I love the chart, too. See if I can keep my three fish alive and happy...
  • George: Perfect way for beginners to learn about aquariums. I will keep the diagram and let my Great Great grandson put it by his tank.
  • EDWARD NUNZIATO: thank you i’ll tried it and let you know how it go’s shoud i add any chamicais to the waterwhen i do a change
  • Arnewld: Guess I’m learning the hard way; My tank will soon be fishless. A few already died with the first water change and the rest don’t look too well. I want to start over again and follow your advice. Do you think maybe I can just remove the fish and start the cycle from there or should I empty the entire tank and start over?
  • johnarthur: Chances are the nitrogen cycle is already seeded because of the fish. If you want to leave the live fish in the aquarium, start changing about 25 percent of the water every other day, and treat the replacement water with a tap water conditioner that temporarily neutralises ammonia. Stress Coat Plus and several other conditioners will work for this purpose.
    On the other hand, if all the fish are dead, remove them along with most of the water, add fresh, conditioned water, operate all the accessories, and wait. You may also want to feed the nitrogen cycle bacteria a VERY SMALL pinch of fish food every other day.
  • Arnewld: Got up this morning and found that all of my danios, whom looked very sick yesterday, were up and about like normal if not better than ever. Wow; I was so happy. I might have taken the first water change a little too far and unintentionally killed the rest, but I hope these little guys survive; I’m only changing 20% water, no more-no less, from here on. Also got the water treatment for the next water change (JohnArthur). Does anyone know where I can print a calendar type data sheet to keep up with the nitrogen cycle; I’ll be doing water tests frequently and would like to record the results atleast till the cycle is established. Special Thanks to this website and the members within.
  • Thomasthecat21: So, basically you drop some food in the aquarium every few days for a few weeks, get a nitrogen testing kit, and when the kit reads zero for both ammonia and nitrates, you can add fish. Right?
  • johnarthur: That’s pretty close. Nitrate should be below 40 ppm, and you may want to do a small partial water change before adding fish. If you add only a few fish at a time, it will give the nitrogen cycle time to catch up with the increased biological load. To maintain a safe biological load, feed the fish no more than they eat in a couple of minutes, and change 20 or 25 percent of the water every week.
    Arnewld: A well managed aquarium usually does not require a lot of testing. If you want to keep records, most computer programs can make charts, or you can just make a list, then copy and paste it several times.
  • Wicked_Monster: I wasn’t aware of this cycle and had been changing ALL the water whenever I cleaned out my aquarium (about every 3-4 wks). I had a quite a few fish (Angel fish, gold fish, tiger barbs, gourami, and a cichlid) and they were never affected. That is until recently, my tiger barbs and Angel fish died on me. I’ve been buying Tiger barbs to replace the original ones but for some reason the new fish never make it past two days! Could this cycle be the reason?
  • Wicked_Monster: Btw my other fish are doing just fine. How strange...
  • kbancroftbillings: I have a 20 gallon tank and my ghost catfish had babies along with one of my platys. I have the fry in a baby net, but I don’t know how many of them I will be able to keep in my tank. I am down to 4 platys, 2 catfish, 2 dalmation mollys, 1 female betta and a neon tetra that was given to me. How many of the babies can I keep? And how often should I be cleaning out the entire tank? I have only cleaned it out totally once before and I have the tank for 4 months. I do a 20% water change every week to keep them healthy.
  • johnarthur: With weekly partial water changes and a reasonable biological load, it’s not necessary to completely break down and clean an aquarium. As for the breeding traps, a large float of hornwort works better.
    WM: Some fish are more sensitive than others to toxic nitrogen compounds. In addition, you may want to look at compatibility issues:
  • JakiNicole: Okay so if you do not have gravel from an established aquarium you can use store bought gravel and just "feed" the empty tank a bit for a few weeks?? I had no idea fish were so complicated! haha
  • appoolshark: with a well planted tank and moderate fish load, do water changes still need to be done if there was a way to effectively neutralize all incoming nitrates? there has to be a way to do this. there’s plenty of ponds with stagnant water that rarely see high volume inflows of water, and both the plants and fish (granted, they’re usually hardier than most tropical fish) seem to thrive.
  • jacquie*09: what a brilliantly easy way to explain the cycling of an aquarium! i keep hearing good things about the IPA Master test kit and have ordered 1, ive started my cycle off with goldfish flakes and hope to have it ready in a few weeks for my baby Axolotl.Glad I found you all!
  • johnarthur: Thanks for your comments.
  • suvajitdas12: hi John this is very gud information for the beginers though I am not a beginer fish keeper but I came to know such valuable information which I didnt know through out my 4 years fish keeping time. thnks a lot..but can u pls suggest me how to check the ammonia and nitrite level of my tank whch should be 0?
  • suvajitdas12: John I have done already a 18"/18"/10" tank recently 5 days back with white sand as substrate and planning to keep parrot fish.can u tell me how much water will remain this tank in "gallon"?
  • johnarthur: To calculate cubic inches, multiply 18 times 18 times 10. To find gallons, divide the result by 231. That comes out to about 14 gallons if my calculations are correct. Parrot cichlids need an aquarium of at least 50 gallons.
  • Hazel: so i loved your explanation and for sure i will follow the right path next time i get a fish but as for my fish now i think it might be too late but still i learned a lot from your blog so for what is worth thanks so much
  • Arnewld: So its been a few weeks and I’m glad to say my tanks nitrogen cycle is fully established; I’m even happier to say that the 4 Zebra Danios, that survived the first water change I did while I was cycling my tank, survived every water change after that and are well right now. I have a new hobby I enjoy very much and thanks to this website, John Arthur and the members I can do it right.
  • Lindsay: I set up my 75 gallon aquarium yesterday. I put the heater to 80F and I have the filter running and have an pump aswell. It’s an unplanted tank and I washed the gravel really well before putting it in, also I treated my tap water. This morning the tank is a tiny but cloudy, I tested it and the nitrite/nitrate are still at 0 (don’t yet have an ammonia reading, I have to buy a test for that). So could this just be a harmless bacteria boom? (I have not put any food or shrimp in the water yet) any help would be greatly appreciated
  • johnarthur: Cloudy water can last for several days as the nitrogen cycle is growing. Inexpensive live plants plants will help establish the nitrogen cycle, as will one of the starter formulations that contain live bacteria. Please don’t believe everything you are told about the instant nitrogen cycle, and don’t add fish before all the toxic nitrogen compounds are controlled.
  • Lindsay: I have the starter formula, I know it says that you basically put it in the tank and you can add fish, but I only use it to start the bacteria growth. How much fish food should I put in the aquarium to feed the bacteria? Thank you for your advice
  • johnarthur: A very small pinch every other day
  • Tpayne56: OMG! Thank you! Your explanation was so easy to understand, that I finally got it! I beleive i have just cleaned out all the good bacteria, eventhough i knew enough not to vaccuum the gravel! thanks!
  • marzboater: It really helps to get an idea of what is going on. Thank you very much.
  • Tpayne56: Hooray, they are now swimming happily again! I used a combination of aquarium salt, Epsom salt (in case of constipation, you never can tell,lol, and it did produce!) and some live bacteria stuff. Cycled the water for 2-3 days. Nitrites down to 0ppm but nitrates is at 40 ppm. I think that may still be a little high, don’t you? Nevertheless, they are swimming eating and carrying on again. Thanks again for the easy to follow info regarding the aquarium cycle.
  • johnarthur: Ammonia and nitrite need to measure zero, and nitrate is acceptable at 40 ppm. Less is better.
  • paulj: At last the entire process in easy terms, thank you!
  • daddyyo74: Hi Johnarthur,
    Even with 25% regular PWC’s my nitrites won’t go down and i shur don’t want to remouve all my good germs with a 70% PWC, i have live plants and driftwood, i feed on occasion my nitrates are at 15 ppm and ammo at 0 ppm nitrie levels are at .50 ppm is there something i am missing and would aquarium salt help.
  • harryhashighpants: the other day my LFS asked me if I knew about the nitrogen cycle
    Even Mum was impressed
  • somen1984: This really useful..
  • bree: good info
  • Joey Burgess: Wow very helpful. Thank you!
  • Crissy: Amazing, this article is so active! Love it! I bought a 5 gal EcoPico a couple of weeks ago, and I’m back to learn some more. Thanks John for keeping up with the new questions.
  • sue: my platties are acting weird the are hidihg on the bottom
  • Geri Owen: Thank you SO much...things seem to be somewhat better...though I did loose the second platy this a.m. The two zebra Danios are doing great. I will buy a tester and hopefully in a few weeks can add some more fish. :)
  • johnarthur: Jephil0 posted this excellent and very brief explination of the nitrogen cycle and said it was OK if I add it to my blog. Many thanks.
    For the cycle, basically, ammonia goes up (bad), then good bacteria grows and eats it. The bacteria turns the ammonia into nitrites (also bad). This will cause the ammonia to go down, and the nitrites to go up. Then you get a new kind of good bacteria, and they eat the nitrites. They turn nitrates into nitrates (not too bad, but you don’t want this to be too high, either). Then you get a 3rd kind of bacteria that breaks down nitrates, and your cycle is finished.
  • cat: Hi there, was being helped last week with my new tank issues and I posted another question but no one has gotten back to me so I thought I would try here regarding My New 3 week old 10 gallon tank.
    So I went and bought the API Master Test kit as was suggested. Yesterday I ran my first tests and took them to my local aquarium shop because I wasn’t sure I was understanding the readings. I also took them a water sample. The person there tested for ph only and it was very low so he had me purchase 2 packets of Proper Ph, 7.0 and a bottle of Start Right with Allantoin. He told me to use both packets of Proper PH for my 10 gal tank and 1 teaspoon of the Start Right.
    Well, after doing that I waited about 6 hours and tested again. My readings came out as follows:
    PH 7.6
    Ammonia .25 ppm
    Nitrite 5.0 ppm
    Nitrate 80/160 (not sure, the colors are very similar)
    Now the PH was seemed too high as well as the Nitrates. So I waited until today and I did another test. I got the exact same readings. I did a 25% Water change 2 days ago. If I understand correctly my PH and Nitrates are too high and I’m not sure if I should use more additives or just leave it alone and be patient.
    This tank is now three weeks old and I’m afraid to add any more fish at this point. I lost 5 fish a couple weeks ago and still have only 1 pleco in the tank but he seems lethargic. He doesn’t move around much and I’m only dropping one Algae tab, every other day.
    Any advice? Please help! Not sure if I’m over reacting or just being impatient. Not sure if I should still be doing partial water changes since I added the Proper PH.
    Thanks a bunch in advance for any help anyone can give me.
  • johnarthur: With fish in the aquarium, growing a nitrogen cycle will take extra time. To protect the fish, change about 25 percent of the water every other day until ammonia and nitrite are zero and nitrate is below 40 ppm. During this time, pH fluctuations and cloudy water are common. The pH changing stuff has only a temporary effect and will thus cause more pH fluctuations.
  • Cat: Thanks for your reply.

    After putting in the Proper PH and seeing such a drastic change (The guy at the aquarium store said it would change gradually) I started reading the info on this site again and other people’s problems. I now believe this guy at the store was just trying to sell me products, he didn’t care about my fish. And this place specializes in Aquariums only. Won’t be going back there.
    Well anyway, I did do a 20% water change on Wednesday and the ammonia came down to 0 ppm but all the other readings stayed the same.
    So I guess I will increase to 25% water changes and be patient which is hard, I would love to see some pretty fish in there, lol. But also, I want to learn how to do this correctly so when I get a bigger tank I will know what to expect. My goal is to have a 55 gallon.
    Thanks again and I will be visiting this site often.
    Cheers and Happy Friday!
  • youngjsampson: This may be dumbed down to be used as an educational tool, but as someone who has recently purchased an aquarium and is at the moment playing the waiting to get fish game, it was quite helpful!
  • Geri: John,
    Here’s my numbers on my tanks from my ph testing this afternoon..11-19-12...what do you think? Please rate my numbers on both tanks...I’d like to add to the 29 gallon tank because the one zebra danio has become a REAL MEANIE right now to the other one. Thinking about getting a few small angel fish. Thanks for all your help!!! This site has helped me more than any place!!!! You are the best!
    10 gallon
    (4 flame tetras and one chinese Alge eater)
    Nitrates 1- 20 (says safe)
    Nitrates 2 - 0 (says safe)
    hardness hard
    Alkanity 80 (moderate)
    PH 7.2
    29 gallon tank
    (0nly 2 zebra danios left...had 6 plus 2 bumble bee platys and a small catfish....they all died during the cycling period)
    Nitrates 1 20 (says safe)
    Nitrates 2 - 10 (danger)
    Hardness - hard
    Alkanity 80 (moderate)
    PH 6.8 (neutral)
  • johnarthur: Nitrite (NO2) and ammonia (NH3) should be zero. If you add fish before this, you should change 25 percent of the water every other day. With no fish, water changes are not necessary.
  • charmedto3: very helpful
  • Geri: Thanks John.....did my 25% water change and added four black skirted tetras.
    The 2 remaining Zebra male one female....the male has become VERY aggressive since the other 4 of the school died...should I go ahead and get like 2 -4 more to quiet him down? He’s about to go into "time" out! hahaha A 5 gallon tank. He is relentless....the female can’t get out and swim about hardly at all. He is constantly chasing her. It’s hard to I"m not enjoying the tank due to being stressed out for her! argh.
    My levels are good!!!! :) Thanks for all your help!
  • johnarthur: A five gallon tank is much too small for a fish like a zebra danio. They are fast and active swimmers. Being crowded into a small aquarium encourages aggression. Although zebra danios are not suitable for your aquarium, a single, male betta would be comfortable there.
  • pratik: i have 55gallon tank and i have 3 albino iridescent sharks , 2 bala sharks , 2 dollars , 2 angels , 1 silver arowana. its been 2 weeks now and water became cloudy.(i only have few rocks) and 2 days before i have installed eheim 2217 canister filter (filter media - ceramic rings,diff. sponges , bio substrat and carbon filter) bt water is still cloudy not have changed much.I have seen many videos of eheim 2217 , they are having crystal clear water... my question is whether is it due to bacteria(good) not present at bio filter media hence effective separation is not done yet??? and how much time it will require to become crystal clear..
  • johnarthur: Some of those fish become much too large for most home aquariums, and some are not compatible with eachother. Cloudy water is often indicative of overfeeding or lack of a working nitrogen cycle.
  • pratik: Hey johnarthur, my tank is now becoming clear slowly.... may be my tanks clodiness is due to nitrogen cycle... I will post you when it gets crystal clear...
  • Geri: Both my tanks are doing great!!!! All my numbers have adjusted to the proper cycling is often do you do water chamges??? I know ive read tbis in here before just cant seem to find it. Thanks for all your help.
  • pratik: How many days will required for cycling of 55gallons tank.... my tank dont hv any plants and live things. Except fishes... partial water xhanges are beneficial or not?
  • johnarthur: Geri: A good starting point for an aquarium with a working nitrogen cycle is 25 percent each week if you feed no more than the fish eat in a couple of minutes.
    Pratic: Since the aquarium has fish but no nitrogen cycle, you should change 25 percent of the water every other day until ammonia and nitrite stay at zero and nitrate is 40 ppm or less. This will take at least a month; it’s much faster without fish.
  • Geri: Thanks John....i think im getting the hang of this....thank you so much.
  • Geri: ARGH!!!! I am so frustrated! I am doing everything right. all my levels are perfect. my water temp perfect. I’m doing my 25 percent water changes. My 10 gallon tank is doing wonderful....all my fish are still alive (from Wal Mart 4 flame tetras and chinese ground cleaner) My 29 gallon...after my cycling finished and I did a 25 percent water change...checked my levels and they were good...I added 4 black skirted tetras...(the 10 gal. has flame tetras so I thought they’d be good for the 29 gal) I put them in the last one died on me! I discovered that their fins had been nipped...alot...but I never seen anything like that happening. Do you suppose these deaths are from bullying and stress from the Zebra Danio??? ****. I’m bout to flush this male danio down the toliet! What is a good fish to tank with zebra danios?
    I’ve had 11 fish from Wal Mart...with only 4 of them dying (during cycling) and 7 of 8 from Petco have died...4 tetras, one albino catfish and 2 bumble bee playts (plus, not counting 2 babies) What is left is a pleco. I guess I need some really strong fish...I hate to keep putting fish in the 29 gallon only to have them die. :(
  • Dee: Hello. This cycle graphic is very good. Thank you. I just want to confirm with you John, about our aquarium prep. We started our 29 gallon aquarium and just had water/filter, etc. going for about a month, no fish. I also put in a sponge next to the filter that came from the aquarium store and had "good" bacteria as she explained it. After 4 weeks we had water tested, all well according to store, and got some starter fish (3). All well, seem healthy and swimming well. AFter one week we got three more fish (last night) after testing and double checking at store no nitrate nor ammonia. So here’s the question. Should I change out 25% of the water starting this weekend? And do I need to add anything to the new water prior to using it? Anything I need to change about what we’re doing? Thanks for the help. (it’s a freshwater aquarium and the temp is 72)
  • johnarthur: Nitrite (NO2) and ammonia should measure zero, and nitrate (NO3) should be less than 40 ppm. A good starting place for aquarium maintenance is a 25 percent water change every week. Frequency can be adjusted to suit the biological load on the aquarium. Replacement water should be roughly the temperature of the aquarium, and it should be treated with a good tap water conditioner. A tight fitting full hood will prevent water evaporation and the subsequent buildup of minerals. Feed the fish twice a day if you wish, but always feed no more than they actually eat in a couple of minutes.
  • Dee: Two more things. I bought last night a Seachem product called Ammonia Alert - says it lasts one year. I had not had a chance to check reviews, so I did this morning and there are quite a few that say this does not work adequately. I can return it, it’s not opened. Any experiences out there?
    Oh, and re: aquarium and waiting a month - my daughter had earned an aquarium by keeping her side of her room clean - then she had to earn the water. Now the fish. That’s where some of the patience has come from!
  • Dee: Heck another question. WE have well water - we have used the water from outside (it does not go through the softener there). Do we need to treat it? We didn’t for the beginning and numbers are fine now. But for adding water should we treat it with something? And what?
    Thanks again. I should be done with questions. For now.
  • johnarthur: It would do no harm to treat the water with a good tap water conditioner like Stress Coat +. Some water softeners are bad for fish and plants, so you may want to bypass it.
  • Dee: Thanks John. Very helpful. We’ll do the Stress Coat +. And I believe I’ll return the Seachem Ammonia Alert - reviews were not good.
  • Gourami Man: Does it still work with fake plants?
  • Gourami Man: I like the drawings!
  • Chia4855: Hello! My common goldfish has ammonia burn but I’m getting prime water conditioner and will do a 25% water change as soon as possible. How can I cure his ammonia burn? Also, what is the best brand for a water test kit?
    Sorry, but last question, in order to keep the nitrogen cycle going, I would have to do about a 50% water change once every week after Gill is healthy again, right? If so, when would I clean his pebbles?
    Thank you so much!
  • johnarthur: About the only cure for ammonia poisoning is good water. This link shows corrective measures:
    Many of our forum members recommend the API master test kit. It has sample tubes, reagent chemicals and color comparison charts. Before doing partial water changes, you should know that large water changes can produce sudden changes in water parameters. The nitrogen cycle bacteria live primarily in the substrate and filter elements, so be careful to not clean them too thoroughly.
  • Geri: Hello....well I’ve finally made it through the whole cycle deal....I’ve learned so much about aquariums during this time...and esepcially here with all the information given and questions answered....thank you John.
    Update: 29 gallon tank: 5 Black Neon Tetras (they’ve been livinin now for 6 weeks) Just introduced 4 Cherry Barbs last friday (all is well) I added sand in replacemet of shells I had in the bottom of the tank last night...other than a bit of cloudyness things are awesome this a.m. Adding sand has eased my desire to have a salt water tank.
    My 10 gallon has been totally awesome since day one. loosing only 1 flame tertas. I added 2 lemon tetras friday...that makes 3 flame 2 lemon. I will add sand to that tank soon.
    My water changes...get fish are compatible to water conditions and other fish....get a bottom cleaner...I am so happy to have started such an amazing hobby. I love my tanks!!!!
  • Joni: I wish I would have read this blog BEFORE we killed 4 beautiful fish of ours. I paid for you to answer my question, but maybe this was the answer... I’ll wait to hear what you have to say.
    Please be kind, we are mourning our departed fish :(
  • johnarthur: Most pet shops don’t bother to inform aquarists about the nitrogen cycle, so we all start out the wrong way. Decades ago when I began aquarium keeping, the nitrogen cycle was not even discussed in aquarium magazines, so my paper route money went mostly to replacing fish. Now it’s fun helping others avoid common mistakes and learning from their experiences. I wish you success.
  • Dee: So I keep asking questions. Tested the water in our 29 gallon today. All is fine. What about aquarium salt? Needed with freshwater? Helpful? Or not of value?
    We still have 5 fish - had lost one dalmation mollie right after christmas - I believe we will wait another week before we add any more fish, and then maybe only two.
  • johnarthur: Questions will get a faster response if they are posted in one of the question categories. Blogs are intended as reference materials and personal stories of aquarium adventures. Here is my opinion about aquarium salt:
  • geri: I recently added 4 cherry barbs my holds 5 black neons...which have been doing fine for 2 months. With in 5-7 days one by one all of them died. I noticed a clear bubbly coating on them. What is that? Immediatly I checked all my stuff...water balance...nothing had changed.
  • geri: Now my Black Neons are dying off...I should of left well enough alone...starting to get really discouraged. HELP!
  • johnarthur: The aquarium probably has water quality issues. Here is how to start correcting the problem:
  • Ms. Eve: arggg, i have a huge 75 gal fish tank and only two fish... a 12 in oscar, Birtha and mr sucky sucky, a placostomus. i hate changing the tank. i have to do it every week... i have plants, two different kinds of lights, lots of bubbles and a bio sponge at the end of my intake tube which fills up with good bacteria... I have to rinse it out just a little every other day or it clogs... I love Birtha... she is like a water bound puppy... lol. But i have said yet, i hate water changes! I use a huge vaccum but still can’t reach bottom of tank with out submerging my arm up to my arm pit.... arggg. Can’t i drill a whole in bottom, and pull the plug once a week or something. lol
  • vicki: I understand it would have been good to cycle with no fish but my problem is I did not do this .Now all I want is to manage to keep my fish alive and get them through this.Please any and all help would be greatly appreciated .
  • johnarthur: Change about 25 percent of he water every other day until ammonia and nitrite (NO2) stay at zero and nitrate (NO3) is below 40 ppm. This should keep the fish safe by diluting toxic nitrogen compounds. Since the nitrogen cycle bacteria need the toxic compounds to grow, partial water changes will limit their food supply. The nitrogen cycle will develop fine, but it will take longer. Pet shops seldom mention the cycle, so most people start with fish in the aquarium; you’re in good company.
  • Geri: Update on my 29 gallon tank. All fish have died...down to the last Black neon...which I finally took out of the tank and placed in a isolation tank. I vacumned the tank. cleaned all the plants etc....refilled the tank...its sitting empty. I am putting a pinch of food in the tank. I was thinking about waiting for about 2 weeks before adding my betta...but I’m scared to death of this tank. All my fish died of ick. All this happened AFTER I added 4 new fish...for nearly 3 months the 5 neons were fine. Within 1 week of adding the cherry barbs they all died. Do you think by doing what I did to the tank that it interuppted the biological cycle? And...if my numbers are all good...that means its cycled? right?
    Or should I go ahead and do 25% water changes for a while?
  • Jeanette: I have a 4 gallon tank with one male beta in new tank for a month. I didn’t know about cycling without the fish in the tank. According to the test kit, my number have been good. I did have higher ammonia when there were 3 neons in with him. The ammonia problem was solved when ate two of the neon and the third one died when I used the wrong jar of water...the one with the hummingbird syrup...instead of the treated water. I changed about 25% of the water but it clouded up overnight and the neon was floating while Freddy was on a sugar high.
    I cleaned it all, used fresh water and put the fish back in the tank. Things have stayed fine with the numbers. I used a pellet food that attached to the side of the tank in hopes that it would be a way to have food in the tank in case we were away a couple of days. It polluted the water. I have turkey basted the debris out but since have developed a thin layer of a film on the water. Along the sides of the tank and attaching to some of the silk plant leaves, are tiny clusters of bubbles. The fish stays near the top and the amount of bubbles is greater in that area. He comes to the top frequently to breathe. When I add fresh treated water every couple of days, he will swim around more.
    Any thoughts in regards to the film and bubbles?
    I will appreciate anything you have to say.
  • Jeanette: I just realized that the little clusters are not bubbles but something that looks like tiny particles of solidified milk. The thin film is a slightly white opaque substance.
    I apopologies for the typing errors in the previous past. Hard to see what I am doing with my IPad.
  • johnarthur: Fish and some foods have oils that rise to the water surface. Regular, partial water changes plus a conservative feeding schedule will dilute the oils.
  • Geri: Can you use the sand that Wal Mart sells for reptiles in your aquarium?
  • Jeanette527: I did a 25% water change this morning and rinsed the filter in the water that I took out and now the water looks great. There was too much food collecting in there when I was trying to f’ind a food that he would eat.. I donated all the food that I unsuccessfully tried out to our local FoodShare. Fish get hungry, too!
    Thanks for the response.
  • Jeanette527:

    I have a 4 gallon Aqueon tank. I didn’t cycle first. I put the beta in December 26. Jan 7 I had to clean the tank out because I carelessly put in the wrong water. All is going well. Right now I just have the dip sticks for checking levels and I am not sure how accurate they are. ( I have the API Master Test kit ordered). The nitrite and nitrates have stayed white on the color coding which is 0 or safe. The ammonia is usually good or ,05...first or second on the color code. If the ammonia goes to the second color I add a bit of water after skimming the slick off the top and any other debris. The fish gets quite active with the fresh water. So my question is, how do I know when it has cycled. If I have missed the answer in the above posts, my apologies. Thanks for your imput.

  • Debbie: Is this the same proceedure for a cold water tank?
  • thea: Yes, a cold freshwater tank develops a nitrogen cycle exactly like a tropical freshwater tank.
  • Cierra: Thanks this helped a lot!
  • Jeanette:

    I got my API freshwater master test kit yesterday. I did the tests and the ammonia was .25, the PH between 7.2 and 7.6, 0 nitrite and 0 nitrate. I have a 4 gal tank with one beta, a filter, and a heater. I didn’t cycle the tank like I should have and put him Iin the water Dec 26. Because I added the wrong water Jan 6, I had to clean the tank, wash everything, and start over with new water. I have been changing 25% of the water every few days...which I did today with added ammonia loc which brought the number down to 0. He seems content and makes bubble nests everyday. So my question is....will it ever complete the cycle?

  • Jeanette: I have a beta, a 4 gal tank, a heater, and a filter. I didn’t cycle the tank before putting the fish in. It has been a month ant the nitrite and nitrate stay at 0. I change 25% of the water every few days and use ammonia loc to control the ammonia.. It has been a month and I don’t see much cycling happening. I rinse the filer in the old water and use a turkey baster to get the debri out.
    The PH is between 7.2 and 7.6.
    Any sudesstions in regards to the cycling?
  • thea: Jeannette. You don’t see any cycling because none is happening. Bacteria feed on ammonia. You have blocked all the ammonia with your ammo-lock so no bacteria has been able to grow. What you need to do is get rid of the ammo-lock, instead invest in an API freshwater master kit and test daily. Change 25% of the water whenever you see -.25 ppm of either nitrite or ammonia. When ammonia and nitrite stay at zero without water changes (for several day) then your tank is cycled. From there on in you can change 25% of the water per week.
  • Jeanette: Thanks, Thea. i guess that has been my problem. I have been using chemicals to neutralize the ammonia as well as changing 25% of the water every couple of days.
    I worry though that since the fish is in the tank , if I let the ammonia climb just a little to breed bacteria that I will in the long run hurt the fish. I see the importance of cycling without fish in the tank.
    I did get the API freshwater master kit the other day and have been checking the water for ammonia frequently. I am assuming that there won’t be nitrite problem until I get an ammonia problem.
    Will I ever get a complete cycle without hurting my beta? He is very content and making lots of bubble nests.
    Thanks again.
  • Geri: OMG! Now my filter/pump system quit....and I have to replace it. So this means I have to go through the WHOLE cycle system AGAIN? Right? I am getting so frustrated.
  • Geri: Do I completely change out the system and replace it with a whole new system? or buy a new set up and use the housing part of the cycled pump? does this matter? Replace the fan? or the motor?
    I have four fish I’ve had since Sept and I do NOT want to kill them...should I take them out of this tank and put them in the smaller tank while this cycle process goes through again...please I don’t know what to do. I’m actually scared here.
  • thea: Geri You do not have to restart your cycle from zero. Keep the media wet (that’s where the good bacteria lives)–if you can fit it into the new filter go ahead,if it is floss you can even cut it up and stuff it, if not, put it in a clean nylon and suspend it into your tank. Leave it in for a couple of weeks and then remove it. The bacteria will transfer and you may not even have an ammonia spike. If you are keeping the gravel — that is the other place where the bacteria lives–I doubt you will even notice anything.
  • Lauren: I have had absolutely no problem with my 4 red minor serpae tetras(probably butchered the name). I started off about 2 years ago with one angel fish, a few neon tetras, and my 4 red minor serpae tetras. The angel fish got harpooned by my cat, the tetras died, and I still have 3/4 of my red tetras.
    I started them off in a 30-50g diagonal tank(not exactly sure, it was a while ago) and now have them in a standard 10-20g tank. I have had also had crayfish in the same tank, about a year ago now. We had to get rid of those, we couldn’t feed them properly.
    I have had 4 red tetras up until now, when one has suddenly disappeared from the tank entirely. Down to 3 tetras, asking my parents for a few more to add into the tank, but would I have to do the nitrogen cycle? I have never done it, or heard of it until now.
    My tetra’s have been fed goldfish flake food that is actually years old... 3-4 years, I think. I haven’t had a problem with it, no discoloration or anything. I do not have tank plants, or other species of fish currently sharing a tank. No problem with nipping, they’ve been schooling since I’ve gotten them. They seem happy as a clam... I usually don’t change the water, either. I just refill it once every month or so, when it is about an inch from the top of the tank, and with tap water. I don’t treat it either... They have eben pretty much just fed and the tank refilled for the past 6 months, and recently vacuumed it. Would I need to take the nitrogen cycle into account here, or just continue doing what I’m doing?
    They’re the only fish that have survived for over 6 months, and now over 2 years. Would adding new tetras disrupt them and stress them out too much?
  • Geri: Well its been 6 months since i first set up my two has been an amazing journey to say the least...i have learned so much. I currantly have a 5 gallon that houses 4 molly babies and a ghost shrimp....they are doing amazing. the 10 Houses my second betta Fin. my first one i lovingly named Sid Fishious Died after about a month and a half of organ was a devastating loss for me. Fin is doing well but his tail is turning black...not sure if it is his colors coming out or fin rot...gesh. he does get tank maintanence every week and im monitoring his tail...will start adding aquarium salt if it continues. The 29 Gallon has finally cycled and causing no more problems. it has the marble molly mommy..a black molly and my Four original tetras. i am finally relaxed and enjoying my tanks...appreciate all the suggestions from this blog...always read up when someone puts in a new blog....good luck everyone!!!
  • Keeran: Thanks. I was not aware of the ‘on-goings’ within a tank in any great detail. I knew that it was good to have plants in a tank but never really knew why. There’s a few other points here that will help my betta tank. Thanks again. Much appreciated.
  • Betta Fan: Cool, I like the picture.... funny. Thanks Johnarthur:)
  • Margie: Thank you for this information. I have only plastic plants in a three gallon tank with a betta a tiny catfish. I am going to get a live plant. Will that help with the film? The fish are very active and healthy looking right now, but I worry about that film harming them.
  • johnarthur: The film is probably oils from fish or food. A three gallon tank is very limited, so try to feed no more than the fish eat in a couple of minutes and change about 25 percent of the water every three days. This will help remove the film, as will surface turbulence from the filter. You can also use a clean paper towel to soak up some of the film. A fast growing plant like anacharis will improve water quality by removing some of the excess nutrients.
  • Peter Ware: Thank you so much I have read this item & found it very helpful in setting up my wifes new aquarium
  • bobby: i read somewhere that sprinkling a little bit of fishfood every couple days can help with with the nitrate cycle. is this true or false??
  • bobby33: this helped me understand alot
  • Beans: Hi - just purchased a 12 litre tank over Easter. Our 3 platies survived 9 days because we didn’t know about the nitrogen cycle - shop owner was just eager to sell us some fish. So this time we are going to do it properly with a fish less cycle. Wish I had seen this site before buying the fish!
    So... We have cleaned the tank, filter, gravel and cave. Have added water with the tap safe stuff. Could you please give me step by step of what to do next, how to make the tank ready, how often to add food to start cycle and when and if I should make water changes.
    Thank you so much
  • k french: Hi,This I can understand!! most of the info i have read i just cant seen to get it. Thank you so much great info.
  • Miamay: Just joined the forum after googling problems about setting up my tank have read your post and although i find the cycle hard to understand, it has beem made a little easier by your blog. Have 120 litre tank and has been cycling for 7 weeks. Readings were showing today ph 7.2, ammonia 0.50, nitrates and nitrites 0. Think we were a litle overzealous and put too many fish in too soon which has resulted in cycle starting again. We water change regulary and gravel hoover. Do you think i am taking away the bacteria before it is established. Should i only syphon water out now until cycle complete. In last 2 days I have lost 3 fish, although my gupply had babies. I only feed every other day. Any advice would be vey welcome.
  • Jeanette527: My tank is much smaller, 4gallon, and I have been working since Jan 7 with one fish trying to get it cycled. My numbers are about the same as yours. I think with the fish in cycle, it is just going to take a long time!!
  • johnarthur: That’s much too long for a four gallon tank to be growing a nitrogen cycle. Please click this link:
  • sassymomma: Thanks for this information. I have two golfish(comets I think) and a pleco, which I’ve had to move twice in the last two months.(not including the van ride from the person’s house who gave them to me, which makes it 3 moves) Thankfully they show no signs of stress, and have survived each move. I make a point to keep half a tank worth of old water to put into the new tank, and put the old gravel, decorations and filter in too. I have fretted a bit over the moves, but the first tank got a crack and sprung a leak, and the one I replaced it with was too when I put them in the newest one last night I simply put ALL the water they had in, which half-filled the new tank.
    I’m sure by now you’ve figured out that I know NOTHING about fish-keeping, these goldies were a Christmas gift which of course, mom gets to care for. Any suggestions on how to settle them in now that I have them in a 20gallon with proper filtration?
  • Rebel: Thank you for explaining how to/what is cycling. I’m going to sure do this for my tank and fish’s sake.
  • yukta: nice blog wow this sketch makes it easy for beginners like me to understand the stuff
  • new b: thank you so much ... very helpful and easy to understand. i am new at this and patheticly thought to fill it plug it in and put in the fish. i have found this club very helpful ... currently having problems and have been corresponding with another member. still alot to learn :)
  • jack0602: helped a lot. thanks
  • jinnylouie: Thank you sooo much for all your help, it was wonderful! I will Be using All you explained To Try To Get My Tank Working :) And Great Drawings!
  • Abee: Fantasic article and has helped a lot. I have just bought a 14 litre fish tank (with filter) and put two regular goldfish in. I left it around an hour before putting my fish in and I added "biological aquarium supplement" along with "tap water conditioner" it has been two hours now and my fish have still not moved from the bottom of the tank. Is this due to stress? I don’t know whether to worry. The fish shop workers told me it should be fine to add them the same day after putting the supplement in to stablise the tap water.
    Wish I had read this forum first and known to wait.
    Any help to a newbie like me is very appreciated.
    Thank you.
  • Jeanette527: I hope they are moving about a little more by now. Perhaps they are adjusting to water temp. Is it Tetra Safe Start that you used? I had great success with that one when used for my betta. Is your water filtered? That is especially I prtant as I understand from others for goldfish.
    You may get some discussion about the size of the tank for two goldfish. I am kind of new at fish keeping myself. There are a lot of good discussions at this site in regards to gold fish and cold water tanks for them.
    Good luck and enjoy your new hobby. I was surprised at how much there was to learn. You might want to get the API water test kit so you can make sure the ammonia doesn’t get too strong.
  • Paul888: An absolutely brilliant way to make it easily understood!
  • Rebel55: I hear of people cycling their tanks AFTER the have added their fish. And since I didn’t even know about cycling when I first got my aquarium/fish, I was hoping if I could do the same. Also, I still don’t understand how to cycle. Why/what do I feed the plants in my tank before I get my fish? I’m just really confused of what exactly to do and use.
  • johnarthur: With no fish in the aquarium, you can feed the nitrogen cycle bacteria with a small pinch of fish food every other day. Here is how to grow a nitrogen cycle with fish in the aquarium:
  • Linda: Very informative! Thanks.
  • RIPtunip: We bought a 19L tank last Friday for our 3 year old. It was a very sudden decision but I wish hubby and I had done our research first. We waited three days following info on the tank boxafter setting up tank with washed gravel, a filter, plastic plant and funny blue fish ornament. We got poor Tunip from a big chain pet shop, the guy there was very helpful saying the first three fish my son chose already looked to be on their way out so we chose the fish at the top, swimming strongly like he was the boss. He was happy for a couple of hours then spent the evening at the bottom of the tank looking sad. He was there yesterday morning, we fed him, after five minutes he swam around and ate then went back to the bottom.. He wouldn’t eat this morning, came home at lunch to find him belly up. I’m actually really upset and not just for my son - he’s happily waiting for Tunip to come home from the ‘fish hospital’ now. Wish I had found this page before we lost our fish. So, the water is really cloudy is this good or bad? if I add some fresh plants, a light and keep testing the water for nitrate will Tunip the second survive?!
  • Madeye: Cloudy water is usually a bacterial bloom. I would do a partial water change, 15-20% a day until ammonia is very low/gone. Speaking of that, I would suggest getting the API Master Test Kit. Good for you researching now instead of never! :thumb-up:
  • About to start: Really informative!!! Just got a tank and i’m doing some research before venturing out to get the fish. This has really helped. THANKS!!
  • Bianca: Hi, thank you very much for the great explanation! I am setting up a new fresh water aquarium now. I had an aquarium before, but did not let cycle the first time.. I definetely don’t wabt to male the same mistake, so that is why I was interested in this article. Question: Should I put flakes in the aquarium for bacteria to grow? (There is no fish yet). If yes, what frequency?
    Thank you!
  • johnarthur: I use a small pinch of flake food every other day to feed the cycle. Others prefer using pure ammonia. With either method, it’s easy to overfeed the cycle and thus make it stall.
  • Riverhawk16: What about for a one gallon fishbowl?
  • johnarthur: The nitrogen cycle works the same in most all aquariums, but its processing capacity is very limited in a small container.
  • kerr81: Excellent and very well written ! Loved the diagram too ! Thank You.Kerr
  • fredister: great article
  • Efrain: Good knologed.
  • Efrain: Hi I have a 125 g tank with 2 emperor 400 & 1 aqua clear 500 & 2 power head with 4 bala sharks, 4 red tail tinfoil barbs, 5 golden tin foil barbs (4 " each) & 7 tiger barbs, I don’t check the nitrate for 4 months & when I check it read 160 ppm, I make 50% water change twice and now read between 40 & 80 ppm, I always do a 25% water change every 2 weeks, I will do a 25% every week to put the nitrate down, any sugestions?
  • Anne Z: Awesomely, hugely helpful!! Thanks! Guess Ill wait a little while for the fish.....; )
  • Debra: OK, so what do you do when you HAD an established for years, then a fish died. With 1 left, I decided it would be a good time to replace the hood (broken light sockets)and change from a poorly working undergravel filter to a side mount whisper (Brand) 2-filter "water Fall type system that works great. Everything was fine and working and testing well, so SLOWLY, over a couple of weeks, I added a total of 4 more fish, what was in the tank originally, when I found it. Long story short...I cannot get the nitrates lowered ALL AT! NO MATTER WHAT I DO! Nothing changes, the SAME HIGH READINGS (COLOR CODED TEST STRIPS) despite treatments of nitrate lowering EASY BALANCE (BRAND), vacuuming and water changes. Fish are stressed, 2 have died! I was taking advise of Petco "experts", going down there daily asking what to do, ended up being told conficting advise like take charcoal out of filter bag, no keep it purchase after another all with the same outcome...NOTHING IS WORKING! STILL HIGH NITRATES, I’ve had them retest my water over and over too. Today I was told the air pump I was told to buy yesterday, is not needed for a 10 gal. tank, but that I needed to start the process of correcting things buy adding aquarium salt. Came home, still tried the air pump and it was so strong it literally blew all my fish to the other side of the tank and they couldn’t even swim, so that is going back to the store, I did put in the rounded table spoon of salt though. Tonight it is still testing the same. The fish who WERE actually pleasantly interacting with me and were all getting along great and their personalities were showing, now COMPLETELY FEAR ME and EVERYTHING THAT I AM TRYING DO DO TO SAVE THEM! They are stressed, are dying and I finally broke down crying at Petco today, Yes over less then $15.00 worth of fish, I cried. I am stressed out too and this is getting expensive with the running total up to $165.00 now (of course that does include the new hood and filter), but still...I could have bought a brand spanking new aquarium...should have, but the fish I had still had always lived in that aquarium since the day I literally rescued the UNPLUGGED abandoned aquarium from a street corner with 5 pink kissing fish in it 5 years ago, 3 did not survive their ordeal then, but the other 2 did (thrived) for 5 years...till now. HELP PLEASE!
  • ahmed: hi Debra,
    IF you can post your question in a new post in the relevent category you can get the advice from many experts. Writing it here, you will only b able to get the reply from the ones subscribed here.
    and i am Sorry for you loss. Nitrates is not that toxic for fish if its under 40ppm. i think the problem is that you changed your filter.
    MOST of the beneficial bacteria that is established during Cycling lives in the filter, You brought a new filter that is totally clean, you should seed it with the material from the old filter so that the new filter can colonise the beneficial bacteria again. Plus may be the total Bio-load of all your fish is more than what the filter can handle. Especially now when the filter is new and still colonizing the bacteria.
    I have read that Test strips are Notorious for giving false readings. see if you can check the readings with a liquid test kit (API recommended). You can get your water test at the LFS as well, but just specifically ask them what the readings are dont trust their "Your readings are fine"
    you readings shall be as mentioned below
    Ammonia : 0ppm
    Nitrite : 0ppm
    Nitrate : Less than 40ppm, better less than 20ppm
    If you readings are not as above especially Ammonia and Nitrites, that is the reason your fish are dying.
    once again i think the problem is caused as you completely replaced the filter. the bacteria in the aquarium and gravel was handling the original bio load and adding new fish increased it. or there could be a disease that came with the new fish. To be sure please verify the Tank parameters that i mentioned above.
    And please post the question in a new topic, that will bring more help.
  • Jeanette: I used a lot of products by API and Tetra but I didn’t start having some success until I switched to Prime. The PH level remained more consistent and the ammonia quit fluctuating. It consistantly stays at 0 now. Give it a try and I think you will see an improvement. I was convinced by many at this site to start using it and they were right. I got it from Amazon. It is made by Seachem.
  • johnarthur: Prime is a good product, but your aquarium should have good water parameters without using an ammonia neutralizer to mask problems.
  • Jeanette: After 4 months, I finally got the water cycled using Prime. BUT, it only lasted for a couple of months. The tank is small...4 gal...and I can’t get it cycled again for these last 3 months. I used the Tetra bacteria starter the last time and it worked in days. But not so much this time. My ammonia, nitrites, and nitrates, all stay at 0. I refresh the water...about 30% of it every 5 to 7 days by vacuuming half of the gravel and adding water treated with Prime. I haven’t been worried about it since the numbers are at 0. I know I should have nitrates but like I said, that only happened for a couple of months.
    Any thoughts?
  • johnarthur: A zero for all toxic nitrogen compounds is just fine. It’s probably the result of frequent partial water changes.
  • Jeanette:

    Thanks. I had decided that it must be okay since he seems to be doing so well. He has been making bubble nests for 2 weeks now. He hasn’t done that for about 6 months. I wonder if they do the nests on a cycle?

  • johnarthur: Good water quality always helps.
  • George:

    I need help, I am a professional that does not have a lot of time. My Granddaughter lives with me and won a goldfish at a carnival last Friday night, by Sunday morning it was floating. I went to the local PetCo and told them they could probably sell me the whole store that I did not know anything about fish the only thing I new was that the baby will be heart broken if I do not fix things. They sold me, a 10 gal tank kit, gravel three plastic decorations, six gold fish and two cleaner fish. so fare four fish have died, I went to another pet store and got some more fish and today I find another dead fish. I have to go get another while she is in pre-school because this one was her favorite! Is there anyone  that can help me get this fixed?

  • johnarthur: They sold you too many fish for a ten gallon tank, and most cleaner type fish have different environmental needs than goldfish. In addition, the aquarium does not have a nitrogen cycle. You can compensate somewhat by treating the water with Prime or another tap water conditioner that temporarily neutralizes ammonia. Change 25 or 30 percent of the waterevery other day until ammonia and nitrite measure zero and nitrate is below 40 ppm. Test the water just before a partial water change.
  • Vale: Great drawing, and excellent introduction to the nitrogen cycle!
  • missemmily: I found this very enlightening.
    I really do wish I would have found this site before I began my little fish-obsession. It would have been helpful.
  • Help me please: This is the most informative information for anyone to know before setting up their first aquarium and for some of us who learned the hard way frm. incorrect information from sales person’s in pet shops.
    Thanks so much
  • dan13: thats the fast way off explaining it all in detail good blog mate all people should learn about this before getting a fish tank..
  • Bobby C: I had no idea of the nitro cycle till reading this about 2 weeks ago, I had some idea of letting the tank settle before adding fish as kept cichlids about ten years ago. This has been really helpful and an interesting read, it’s hard not to add fish early as I’ve been chomping at the bit!! Best to be patient ( not my best virtue) sure it will pay off in the end!
  • Candace: Hi there.
    We have a 10 gallon tank.
    At first we had our beta in it but decided to put other fish in.
    So we moved our beta to a 3 gallon tank.
    We kept the beta in the 10 gallon for about a month, in that month I did 2 water changes. About 25-30%
    Went to to the pet store. They told me to let the tank establish(which is why we waited a month)
    I took the beta and put him in his new tank.
    The next day, went to the pet store and bought an algae eater, catfish and 3 mollies.
    They told me to come back in about a week or so and I could add more. Went back about 10 days later n I got a Mickey Mouse fish and two neon tetras.
    We had one Molly who kept attacking the other fish.
    It’s been about a month and 2 weeks ago our Mickey fish died.
    Then today I came home, one Molly is dead along with the two tetras n the algae eater.
    Is this the water quality? I did research n it said change the water every second day until tank is healthy.
    But I’m wonder, should I be changing my filter? Water temp is steady at 23 Celsius
    I also have fake plants but I’m thinking real would be better? What is the best beginner plant?
  • Vale: Hi Candace, Try copying your question into the green "Ask a Question" box in the top right corner. You’ll get more answers in the forum :)
  • ak1225: Im am so glad I found this!! This article was so helpful for setting up my tank.
  • mentalpaws: this article was SO very very helpful because it was easy and simple. No over my head terminolgy that as a new aquariast I would never understand! Some articles are written for experienced people in such a way (with abbreviations, terms i never heard of etc) that i just don’t follow. I waste my time reading it, when i could be caring for my fish. your article was so easy.
    anyways, i just tested my parameters and for the first time ever they are almost normal !!!!!!!!!!!!!!!!!!!!!!!!!!
    AMMONIA is dropping to .5 it had been 8.0 forever... had a goldie die yesterday.... nitrites are 0 YAY —- Nitrates are maybe 3.0 maybe up to 4.0 or 5 (hard to tell its between colors)
    pH = 6.4
    BEST READINGS I’VE HAD IN MONTHS. I’ve been using a ton of bio stuff like the little white biomax beads you place in the filters, tetra safe start, black activated carbon, PRIME double dosage, a brand new bio wheel filter, (i think my old filters were faulty) things like that.
    i continue with 25% PWC’s every day, till ammonia is ZERO and will never give up. AFter my goldie died yesterday, i did a 90% change. That leaves me with 1 fantail goldie in a 20G tank. Ammon was 8.0 !!
    Do you recomend aquarium salt? i heard its good for gill function, to releive stress and something else, but i’m afraid it messes with the nitrogen cycle.
  • johnarthur: Salt can treat some maladies in a freshwater aquarium, but it’s not a cure-all or a substitute for good aquarium management. Besides, they’re called freshwater fish for a reason. I don’t recommend large water changes, because they can cause sudden changes in water parameters and thus stress the fish. If you are using Prime, you may want to use only the recommended dose. Since Prime temporarily neutralizes ammonia, a 25 or 30 percent water change every other day will get toxic nitrogen compounds under control. Water tests done just before a partial water change will give a better picture of conditions than will a test done just after a partial water change.
  • siva: Hai friends I am new to this. Please help me. What is nitrogen cycle bacteria? Where can I get it?
  • johnarthur: Some aquarium shops sell starter formulations containing the live bacteria species that make up the nitrogen cycle. The bacteria is also on raw fish and shrimp, and decaying fish food will encourage its growth. Start with very small amounts.
  • witcharoo52: This is excellent! I learned a lot of what Im doing wrong...will certainly correct and hopefully keep my fish alive and well.. thank you !!!
  • Mark: I have a small fountain with aquatic plants, but no fish. I added commercial cycle starter and let sit for a few weeks with occasional partial water changes. I then got 10 gal and 4 gal aquariums and hooked them up with a small pump and siphon return line. I used some fountain water, RO water and plants to start it. After a little fiddling with chemistry it was pretty good’ EXCEPT there was moderately high nitrite. No ammonia, no nitrate. After a week (I know, too soon) I put in 3 small Chinese algae eaters, two small Corey catfish and 4 ghost shrimp. I continue to have nitrite, but no other probs. I’m doing water changes hoping it will get better. This my first aquarium, but I’ve been studying the internet! Any ideas?
  • Joni: Yes. You should start a new post on the main forum. Is a great question. Also, your chinese algae eaters will eventually kill your cory by sucking their slime coat off.
  • JoseL: Thank you for your good advice!!
  • Shane Mc: Great post!
  • Tina: Hi there, been reading all the comments so very
    InFormative it’s been an eye opener, I had kept fish in the past and I have been kinda lucky I guess, but 12 years on I have another tank a juwel rekord 800, it’s says I can put a couple of Hardy fish in after 3 days! I’m a little nervous about doing this, after 24 hours the tank is cloudy, I’m assuming this is the beginning of the nitrate cycle? What are your thoughts and should I put a pinch of flaked food in to feed the bacteria? Thank you in advance.
  • johnarthur: I like to add a very small pinch of fish food every other day to feed the nitrogen cycle bacteria. An aquarium is safe for fish only after ammonia (NH3) and nitrite (NO2) remain at zero concentration and nitrate (NO3) is well below 40 ppm. Cloudy water usually means the nitrogen cycle bacteria are starting to grow.
  • Tina loulou: Thank you for the information, I’m beginning to wonder if I need a stress enzyme for me!! :) someone suggested it might be my decorations causing the cloudy water, I brought them from reputable suppliers, so I’m hoping it not them! Once again thank you.
  • johnarthur: You are very welcome. Cloudy water and fluctuating pH are common while the nitrogen cycle is growing.
  • netty: so glad i read this i bought my son a fish tank and was told to wait 3 days before getting a fish but it went that cloudy i washed it again, ive done it 3 times so far then my friend said her husband waited over a week and it cleared up, so googled it and found this website. ive left it 5 days and it looks like its clearing again. ive just told my son to go and put a pinch of food in it. :-))
  • blackwood: that is so helpful sir. thank you very much. :D
  • Kolyabean: THANK YOU!!! You actually explained it in English! I didn’t even know about this part of keeping fish until after I got them and everything. :( I don’t think they are going to last long, but now I know for next time. WHY isn’t this said more? I did a lot of research before actually getting my fish (guppies) and there was NO mention of cycling at all. First my plecostomus died and I thought it was just a fluke and then a day after I got my guppies one died and all the rest started getting all flaky. There could be more to this but not cycling is probably part of the problem! When I did find out about cycling and I did some research I didn’t understand at all and now I do thanks to your blog!
  • Caroline Borg: I was cycling a 90 gallon new tank with an Oscar and 2 angel fish. It was taking a while. I went to my local fish place (not petsmart or petco) and he gave me "a bomb" a bag filled with nasty stuff from one of his tanks. Problem solved.
  • Colin: Nice easy way to read it and understand, however, what about the first WC? When Nitrates are really high?
  • johnarthur: If the aquarium has no fish, partial water changes are not necessary. The third beneficial bacteria species converts most of the nitrate NO3) into plant food. Nitrate is considered safe in concentrations below 40 ppm, but lower is better.
  • ruth: I’m setting up two new tanks: one for African cichlids with a sand substrate and one for South American cichlids with gravel. I wanted to run a fishless cycle to get all the good bacteria in place. I couldn’t find pure ammonia to run the cycle so have been using fish food. The African cichlid/high-pH tank finally got down to 0 nitrites after 6 weeks (it took two weeks of daily food input for the ammonia level to really climb, and four weeks to cycle after that). We added fish, and everything is running great: no ammonia or nitrite/nitrate problems. The other tank is still not ready, after more than six weeks. The ammonia level has finally dropped to zero but nitrites and nitrates are still sky high. I’d judge I’m still a week or two away from having that secondary group of bacteria establish itself fully. My question: is it better to wait it out, or could I speed things along in the second tank by switching the filters for the two? Would that jeopardize the bacteria colonies in the established tank too much? Would switching the carbons help, perhaps? Thanks for any input!
  • johnarthur: The nitrogen cycle bacteria live primarily in the substrate and filter elements, so borrowing some of either or both will introduce more bacteria. However, since the late cycle is in its final stages of growing and the early one is just established, the best option may be leaving things alone. You may want to add some of the fish to the cycled tank then wait a week before adding the rest. This gives the cycle time to grow in response to the increased biological load. At that time it may also be safer to bowwow some bacteria if needed.
  • matheny00: Great article and they art is fantastic
  • ruben: Where do you get the bacteria? Are they always there? i have a filter. please help.
  • Madeye: The bacteria will grow themselves. If your filter has been running for while, you should see brown icky stuff. That is the bacteria.
  • Jacquie: Is Jungle aquarium conditioner good?
  • FishGeek: I wish I would have known about this site when i first started. I struggled at the beginning until I finally did some research, now all is good in my tank, my ammonia spiked and had no one explain to me what that meant. I’m very glad I found this site, very good people and very good info
    Current tank:
    20 gallon
    4 neon tetras
    2 variegated guppies
    1 mickey mouse platy
    1 rasbora het
    in a Finding Nemo decorated area
  • Murphy: Anyone have advise for power backup in case of power outage?
  • johnarthur: Battery powered air pumps are available, and they can be fitted with rechargeable batteries. Air pumps will power filters as well as aerators.
  • Murphy: Can you expand on the air pump powering the filter?
  • johnarthur: Here is how an under gravel filter works. Other types of air powered filters use the same method for moving water.
    An under gravel filter is a plastic plate with lots of small holes, one large hole and feet that keep it about 1/4 inch above the bottom of the aquarium. The large hole accepts an uplift tube with a small air tube inside. As bubbles travel up the uplift tube, they carry water, which is drawn through the substrate and the small holes in the filter plate. The substrate should be at least two inches of 1/8 to 1/4 inch diameter gravel. A small air pump provides the bubbles, and flow rate is easily adjusted with valves in the airline tubing. During weekly partial water changes, syphon any debris off the substrate surface, and deep clean about 1/3 of it. The bottom plate does not have to be an exact fit with the aquarium bottom.
  • BackInTheHobby: This is a fun and great way to show how the cycle works. Visual aids are great. I like this for kids and adults. I am going to share this with others. Thanks for sharing.
  • myale: I had fish before in my 26 gallon tank. Like the others who commented, I did not know about cycling and they all died. I emptied the tank, but kept the old filter. I’m thinking of getting new fish now, and doing it right by cycling. My question is does the old filter help the nitrogen cycle?
  • myale: And my past fish got ick, so is there ick in the filter that could spread to the new fish?
  • Jacquie: ick could still be in the filter just clean it out really good dont use soap as it will harm the fish you can use vineger but make sure after you use it that you wash it out until the vineger smell goes away and when starting the tank just put a couple drops of ick medicine in it (the blue stuff)
  • Linda Rustad:

    Hi am new to this site but have learned alot.but I need help. Have a 29 gallon fish tank with two goldfish in.thought it was cycled but I guess not because the numbers are whacky. How do I get through this period without hurting my fish.need correct procedure for the cycling tank and how much to vacuum. Thanks

  • Yolanda: Have a look at this:
    Also, it might be a good idea to start a new thread in either the cold water fish or general freshwater questions forum (click on ‘categories’ near the top of this page to get to the forums :) ). Responders will need to know what the results of your tests have been, what your maintenance schedule (water changes etc) is, and how long the tank has been set up to best help you.
  • erincdot: What do you consider a good water conditioner? Is there a brand you prefer above all?
  • Jeanette: Prime is very good.
  • johnarthur: Prime and Amquel will temporarily neutralize toxic nitrogen compounds, and that’s especially helpful if you are growing a nitrogen cycle with fish in the aquarium. For routine partial water changes, Stress Coat is good.
  • KrisSilver: Nice diagram! I use both Prime and Fluval conditioners, and do a 25% change once a week.
  • johnarthur: If the aquarium has a working nitrogen cycle, there is no need to use two tap water conditioners or to overdose either.
  • Mantha: Would you mind answering my question?
  • harpomic: If you get a good bio filter it helps alot. You can buy three stege filters that eliminate ammonia and nitrates as well as particles and wastes. This when cycling new cartridgess every month allows you to be able to have to only change water every two to three weeks.
  • zacsmimi: LOVE your drawing and explanation!
  • faqbdy: This is an excellent article. Breaks it all down nicely
  • grungegirl77: That was great as I am just starting a new set up and need to cycle. I plan on getting just one male betta . I have never used real plants any suggestions ?
  • faqbdy: I was told anubias were great beginner plants and good for betta tanks
  • Lizzy: I am new to this site and was given this Link by Johnarthur and am really grateful to him because now I know what i need to do. I have a 20 gallon tank and am going to get the plants up and running before i get any fish.....Great Job!!! Now i’m off to check out info on the right plants.
  • Tim: I completed the nitogen cycle and I have never done a water change or changed my filters in about a year. Just don’t **** with your tank and bacteria take care of everything.
    Lots of gravel and lots of plants.
  • Tickbox234: Tim, what fish do you have? Not changing water is very bad, really bad!
  • Tim: An angelfish, redfin shark, couple types of tetras, wild snails, rapheal catfish, common pleco, 3 Siamese algae eaters, guppies, swordtail, mollies, two killifish, some other catfish and more which i probably forgot about. The only time you have to change water is if you don’t have plants, I have A LOT of plants. testing my water comes up perfect every time.
  • johnarthur: Healthy, live plants do ingest toxic nitrogen compounds but not enough to substitute for partial water changes. This simulates flow through of freshwater enjoyed by natural aquatic environments.
  • Anna:

    I obviously have no idea what I am doing. My 2 goldfish were fine yesterday morning ..tonight in fishy heaven. My tank had been used before My Dad used it for a long time..what is new is the plants I think I do need to replace these because I read the plastic ones may not be good ..the tank is still running. in your article it indicated to not add fish for 3 weeks the good bugs get in there themselves and I am still suppose to put the flake food in it? should I keep the pump etc running? should I drain the water that the fish died in? and start over? any help would be greatly appreciated.

  • GarryJ: Hi Anna
    Sorry to hear about your losses. You have responded/posted on a Blog. JohnArthur may not see it. If he doesn’t respond in the next few days, please post your own question on the forum. You can do this now if you wish. Hope I have helped. Send me a PM if you are stuck with any of the above. Gaz
  • Landa: I purchased 3 feeder gold fish. One died and the other two lived for 5 years. I have no gravel just because I wanted a visual change. Then I purchased a live plant and a parasite hiched a ride and all the fish died in 3 weeks. No medication had any effect. Cleaned tank and bought two more goldfish. They were fine but bought one more gold fish as I have a 55 gallon tank. New fish had ick. It spread so fast all fish died in two weeks with medication to no effect. Gave up gold fish. Threw away all decorations and let tank try out for two months. Ordered new fish tank decorations and filled the tank and let the pump/filter and aireator run and let the tank set for two months. I have a high end test kit. All the time tested the water and it was fine only high in PH. Asked around and was told by Reef Connections that all of northern CA. has high PH. I finally purchased three male guppies (or so I thought) and ten Neon Tetras. Two male guppies died after one turned out to be a female with not a single sign of being pregnant. Found a very tiny fry and one week later , after being relentlessly being pursued by the remaining male it died. Not a singe sign the male was a female. No large black dot near its rear end and had a long black flowing tail with back vertical stripes. The fry is still alive and though growing slowly is doing great and is getting a touch of color. I hope its not a female. Its just about the size of a small Neon Tetra. I have a 55 gallon tank , with a double charcoal filter and also an aireator. Also have a UV sterilizer. I take the long necked fish net and stur up the water and use the net to scoop up any uneaten food. I add tested tap water to fill up the evaporated water. About every two weeks do a 25% water change and change the filters also. So far no more fish have died. What do U think of using distilled water as part of the water change? I thought it might help with the high PH problem. I feed the fish twice a day and do my best not to over feed. Its hard as they seem so Hungry! Thank you for your time and attention.
  • Jacquie: I think that mabe the goldfish were not in quarantine and so they had brought Ick and fungus also were the plants used before? Because if they are used they can have paresite eggs on them if not they could have just grown there. Did you turn off the lights during the Ick problem? If not the Ick will feed and grow of the light.
  • Petals: "If this blog had a second title, it would be “How to Not Kill Your Fish.”"
    LOL! Awesome John! Thanks for posting this!
  • Joyce Ann: Thank you very much this was very helpful.
  • gerry: Hi.
    Thanks..I enjoyed it..very instructive.
  • rmullick3: hello,
    sir is there any another way to kick start nitrogen cycle in new aquarium without using any manufactured bacteria form market . plz suggest me
  • Jacquie: You can use amonia or get one inexpensive fish to help it start
  • johnarthur: Using sacrificial fish was a common way to start a nitrogen cycle some time ago, but when those sacrificial fish get sick, they leave behind a legacy of inactive diseases and parasites ready to infest a fish with a compromised immune system. Some aquarists use pure ammonia (NO ADDITIVES) to feed a growing cycle, and others prefer using a small amount of fish food. It’s very easy to add too much of either, and both methods have disadvantages. I prefer the fish food method, because I’ve used it several times and know roughly how much to add. Besides, ammonia is a potent toxin.
  • pennylee: a little confusing this starts out saying feed the fish but half way through you say but do not add fish yet. are you cycling with food? Is that all there is to it? Just sprinkle food in everyday? it is not explained very well are there water changes involved do you top up the water thanks
  • johnarthur: For convenience, I use fish food to cycle an aquarium and do not add fish until the cycle is established. It’s too easy to add too much fish food or ammonia, but a very small pinch every other day seems to work well. Nitrifying bacteria occur naturally. Thus the starter formulations are not absolutely necessary, although they will help establish a cycle in less time than just fish food or pure ammonia.
  • MarinelandNeon: I never actually worried about how much percent I of the water I took out. I normally take out 45 percent of the water sometimes more, my fish didn’t die if I use the same filter, I didn’t change the filter after a month has passed.
  • MarinelandNeon: basically if you have your fish tank water established and there’s good bacteria and you change the filter only once a month and change the water once a week and after the last month when you change the filter or if you change the water weight two days before taking out the filter to change the new one. and at the pH drops once a week and conditioner once a a week or month.
  • suekg: This is pretty cool! You couldn’t have explained it any better! Thanks!!!!
  • MarinelandNeon: you’re welcome hope things go OK
  • johnarthur: Most of the nitrogen cycle bacteria live in the filter elements and substrate. Changing or thoroughly cleaning either can stall the cycle.
  • Lynette Bost: Thank you,this the best explanation, I have read so far! Easy to follow and understand.
  • Say2Bubble: its a very helpfull one for those who are new aquarists..... like me.... :) and now i have a question...that can daily changing of the water of aquarium(small size) prevent this problem or it may harm the Fish?
  • johnarthur: If you change 1/3 or more of the water every day, the aquarium may never grow a nitrogen cycle. The same toxins that harm the fish also feed the nitrogen cycle, and a daily partial water change will keep them too diluted to harm the fish or feed a cycle. It’s not the optimum situation, but that may be the only way to handle a small, overcrowded tank. If you change 25 or 30 percent of the water every other day and treat the replacement water with Prime or Amquel Plus, you may be able to grow a cycle unless the aquarium is just too crowded.


  • eFISHient: This is an absolutely fantastic read, as well as visual! I printed and posted it next to my tank in my classroom - it has helped my seventh graders understand the importance of care with the tank more than ever! I always tell them how when you feed the fish you are really feeding the tank! This article and illustration support my saying! Thank you.
  • from Marineland neon: I’m glad all this stuff has helped I still have my 12 fishes in my 10 gallon tank. I’m almost at a year and a half and they’re still happy. I’m offline so thanks for the comments
  • halz: Well I thought that was very informative especially to a newby like my self I found it easy to understand with out it being to condescending lol 😉
  • johnarthur: Thank you for that comment. The blog was intended to be helpful but not too technical. In many ways, the nitrogen cycle is key to successful aquarium keeping, and it’s too bad so many new aquarists started out knowing nothing about it.
  • mandar:

    visit to for more details.


    Sorry posting advertisements to a different web site is not allowed.


    Mod team

  • elaine8073: Great read and so easy to follow. Excellent information in all the comments too - huge thanks !!
  • johnarthur: This is something of a milestone: just over 1/4 million readers of this blog. Thanks to all of you.
  • Jack Chessher: It deserves every view it gets!
  • Mr.Moo: That was great!! I have been running my aquarium for 3 weeks and have not put any fish in yet. I got a test kit and my no2 was 10 and no3 was 160+. I fixed it and now I have 4 happy angelfish.
  • Emi: This is very helpful. I kept my black moor in a 10 gallon for his 4 year life. I was a novice. I’m still not entirely sure what happened but I learned about his tank size requirement. Lesson learned-no more goldfish until I get a 50+.
    We have another 10g that was overstocked and stocked incorrectly. We were told that they could be fine together. Pleco, catfish of some type, Redfin, and a dragonfish (yes we have learned our lesson there). Now the tank is with pleco and Redfin. We tried to add an angel but it didn’t make it. Pleco and Redfin are happy alone. (Redfin will be moved when we get the big tank this summer.)
    I had my betta in a 3 gallon who’s water STAYED cloudy. I think it was the tank itself. Like a plastic breakdown. We cycled the new 10g tank for a week with some tetras and they died. When they were removed, the tank went cloudy. It stayed cloudy for a week and instantly cleared up overnight. I tested it and all seemed fine. I added my betta (currently alone) and he’s happy as a clam. I might add a few neons next week.
    I am heeding the advice here for a fishnets cycle for a big tank I may be getting for oscars! I need to more research on the upkeep of them and a large tank but I have time.
  • Christy: Fabulous article. Well written, funny and helpful. A pleasure. Many thanks!
  • Mr. Tickles mom: Will the Quick Start I bought at Pet smart allow me to not put fish food or raw fish or raw shrimp for two weeks and just set up the tank and add my Betta right away? This info you give here is really good and easy to understand about the nitrogen cycle thanks!
  • johnarthur: Quick Start may help seed the nitrogen cycle, but the aquarium is not safe for fish until ammonia and nitrite measure zero and nitrate is well below 40 ppm for a few days. Only then is the nitrogen cycle working. An instant nitrogen cycle usually does not happen.
  • Hjorg: Do we do partial water changes to a new tank even if the cycle is not complete? Vacuum at all? We have 2 3 inch blue haps, tank is only 4 weeks old.
  • johnarthur: If there are no fish in the aquarium, partial water changes are not necessary and will only slow the growth of the nitrogen cycle.
  • Mr. Tickles mom: What do you think about stability? Is it true that stability will live through ammonia and nitrate levels that would kill the natural bugs, thereby saving my fish?
  • johnarthur: Usually, things like Stability are not necessary to keep the nitrogen cycle working and the fish safe. Here is how to start a cycle with none of that stuff:
  • Fish Tank Noob: So inorder to go thru the nitrogen cycle I needs to get a few hardy fish and some plants????
  • johnarthur: NO! Please click and read the link posted in my previous reply.
  • guestallison: Extremely helpful, thank you!
  • Aquafish1: Great job! Very helpful and useful!
  • Lotus: Nice Job, Very Useful!
  • A fish expert: Good Job!
  • Owaiz: Hi, thanks for sharing the link , the filter and the sand substrate that I am using in this tank is from a well established tank, and this tanks levels all seems ok now,and I am going to leave it for cycle for 1 more week,please advice me what beneficial bacteria I can add if it’s required, and let me know what’s good for my plants.moss and water wisteria.since I already ordered neon tetras and glow lights and these plants. I have to figure out how I can place them all . I need your help. Thanks
  • johnarthur: Just add a small pinch of fish food every other day, and it’s OK to add plants right now.
  • cats and fish: this is the cutest!
  • Authority Aquarium:

    I remember reading this years ago when I was first setting up my aquarium!

  • David: So after I get the cycle right on my aquarium, I can add fish.? do I after everything is okay and I add fish, I have to change 25% of the water every week, forever? My aquarium has set up in my storage for about 5 years covered with a cloth. I will wash it out, before I cycle the water in the tank and get all the readings, right, before I add fish.
  • johnarthur: Before you add fish, be sure ammonia and nitrite measure zero and nitrate is well below 40 ppm. Standard aquarium maintenance includes a 25 or 30 percent water change every week or so. You should also avoid overcrowding, overfeeding and compatibility issues.
  • Leslie: How long should I wait before adding a gold fish to his new and bigger tank after adding the conditioner?
  • Kfaddypa81: Thank you so much for providing such informative and easy to read information. We started with a carnival goldfish that we didn’t think would last a month in a bowl,to having a filtered aquarium and now troubleshooting our fish issues over dinner. Great resource!
  • Su R: Thank you so much for explaining it all................... after so much time wasted, reading so much stuff online and hearing everyone’s various different opinions on Cycles......................... I finally get it!
    My hair is still on my head, I have not had a nervous breakdown and finally, I can enjoy keeping fish and aquatic life!!!!!
    You are wonderful! :-)
  • Carley: He is wonderful. Years of his input into this Club has helped hundreds and hundreds of people.
  • SuR: I can’t tell you how grateful we are!
  • SilverGreenZ: Thank you, that taught me alot :)
  • Bob Hutcherson: This is a very good Article, To bad they don’t have this up in pet shops to
    help the newcomer to keeping fish great hobby.
  • KKN: This explains why it’s important to keep too much ammonia at bay by creating a balance. My question is if I do 100% water changes frequently is that fine? Do people not do that because it’s too much work or because it’s bad for the fish? What is bad about changing water too frequently as it’s related to the fishes health.
    Thanks so much!
  • Su R: Hi
    You need to leave the good bacteria in the water and substrate? Definitely not good to do 100 % water changes 🙄
  • johnarthur: In addition, a large water change can suddenly change water parameters, and that’s very stressful for the fish.
  • Kat: Today I bought uv sterilizer mean green fits on my hang on filter in it is polyfiber. Cleaned my cannister, put the porsulin media on top of chemi blue rinsed, and polyfiber added one new live rock. Before that took out 5 gallons of salt tap water with prime salt level was 23 now is 20 55 gallon filled to top. Wave mKer added also. Have a cheap heater maybe 20 lbs of live rock tank is been going for 8 months lost two anemones corral started growing then died. I have 3 clowns one corral angel one snail clean up crew passed when I used api algae test strip says nitrate higher now about ready to give up with cloudy water if I spend money for water and do good cleaning 50% water change is this cloudy water gonna go away? My skimmer alwYs skimmes but leaves two many micro bubbles. I want crystal clear tank with fish and corrals or just go back to the easy fresh water. I have not done good wayer change on long time.
  • muhammad firdaus: hellow, nice article.
    i get many information from this blog.
    best regard, scaper indonesia
  • Velvel: Thank you so much! You answered questions I had about the nitrogen cycle, plus questions I would not have thought to ask. Best of all, you corrected misinformation I had received at my local fish stores.
    Portland, Oregon

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