Using Citric Acid To Remove Water Marks And Limescale From Your Aquarium

Vitamin C Galore - 01Creative Commons License courtesy of mrjorgen

So I’ve mentioned briefly in a thread that when I cleaned out my new “used” tank I used citric acid to clean the glass up and get the tank sparkling again; I must note this is not a disinfectant but it is mighty good at getting rid of limescale and residue on the glass and a way of cleaning your tank which is safe and will not use harsh chemicals that could ultimately harm your fish.
NB: If you are looking to remove any unwanted nasties from your tank, one of the easiest things you can do (if you don’t want to use chemicals) it sit it in the sun, most things cannot survive being dried out or the UV rays from the sun.

Let me set the scene - You’ve bought a new, used tank. It was a great deal, you got it nice and cheap but my goodness those water marks! That thick layer of limescale! Yick, and if you live in a hard water area the ongoing process of getting rid of limescale from all over the show is a constant battle, especially from that protective cover you have over the lighting, what a pain!

My friends, let me introduce you to Citric Acid and a few interesting qualities it has.

  • This weak organic acid will dissolve limescale in moments.
  • The reason I’ve attached a photo of lemons, oranges and limes is that it is found in these fruits and makes up about 6-8% of the dried fruit of lemons and limes.
  • Food Grade (it must be food grade as industrial is too concentrated) citric acid is safe to eat and very few people are allergic to it. You know those sour sweet with the white coating? You guessed it, that’s citric acid.
  • It occurs in the metabolism of almost all living things. We produce nearly 2kg of it in our bodies on a daily basis and it is quickly metabolised.
  • It is used in some DIY CO2 Kits
  • When combined with sodium bicarbonate you get bath bombs!
  • It is used in “setting” photos in the development process.
  • In industry it is used to dissolve rust from steel
  • Used in cosmetics it regulates ph and is used in the “chemical” peel process.

You can buy it in most supermarkets or online, either is fine. We buy ours in bulk online as we use it all over the house as we live in a hard water area. We have to descale our kettle once a week! But let me tell you about how you can use it in regards to your fish. It does take a bit of creative thinking if you can’t soak whatever it is you are cleaning in very hot water. From this, I make do with some thick rubber gloves and water that is as hot as I can stand it. Combined with a couple of table spoons full of food grade citric acid and you’re set.

1. Get a small bowl or jug you use only for your fish.

2. Boil some water in the kettle

3. Add a few table spoons of citric acid to your container

4. Pour the water over the citric acid slowly, add a little cold water so it’s comfortable.

5. Get a new, clean sponge that will only be used for your fish tank

6. Without using the scrubby side, dip it in the water and slowly wipe down the limescale deposits.

If you have a thin layer of it, it should just wipe off on the first go. If it’s a bit thicker it may take a bit of scrubbing. In these cases I put a little of the granules on the sponge and press it on the limescale. If you’re doing this on glass, you should see the limescale fizzing off on the other side. If you have VERY heavy deposits, you’ll need to get some lemon juice, paper tissue and citric acid. Mix a little lemon juice and citric acid and soak the tissue in it and then leave it on the heavy deposits. It should fizz off within a short amount of time, after that, use your sponge and water solution to wipe it all down.

If you are using this on tanks with fish, please do be careful not to get it in the water in great amounts. It may be a safe alternative, however it does not mean you should be careless. I use this to clean, however I do not allow it to go in the water if I can help it. I carry out this kind of cleaning after I have taken the water out so I can wipe down the water line, then I give that area a good wipe with old tank water before refilling the tank. (Keep the old water next to you then you can rinse the sponge after using the citric acid solution)

If you have removable components, you can make up a citric acid bath and just place the object in the bath to let the limescale fizz off, I do this with the protective cover for my lighting to keep it clear so as not to restrict the amount of light my plants get. My mother always likes adding a bit of bicarbonate of soda for fun, but it’s not necessary. Give the components a good rinse after and then a dip in old tank water or dechlorinated water just to be sure then dry it if it’s a lighting cover.

I hope this hasn’t been too wordy for you and that you’ve enjoyed reading about citric acid. I hope it helps some of you in the cleaning of your tanks - anything to lessen the amount of effort in maintaining our tanks is a bonus in my eyes. It leaves more time to enjoy our fish!

Let me know if you use this method or if you need any help, I’ll try and answer your questions as best I can!

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


  • ethanFish: I have noticed this in my tank so this helps a ton! I will totally try it out. Nice blog!
  • Andtheivy: Thanks ethan! Let me know how you get on!
  • Vale: Great blog, I never knew citric acid could be so useful! Sounds like a great cleaning alternative for anyone who lives in an area with hard water!
  • ReallyConfused: Thanks so much. I have an used tank that looks really crusty. I’ve been putting it off. Great idea
  • blackmoor193: Wow nice blog andtheivy!!!.
    Can we use this on out side of glass to clean water marks??
    With fish inside?? Sounds like silly question eh?
  • Andtheivy: If you have a really hard water mark yeah, just finish it off with some normal window cleaner and a good buff with a microfibre cloth and that brings the outside of the glass up really nice!
  • blackmoor193: Thanks andtheivy!!
    Again nice blog!!!!!!!

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