So I wanted to know how much i should change the water of my tank and if I should leave some of the old water in there and just replenish the rest with new water? I noticed that the water level in my tank is getting lower.
I don't think you want to do a full water change, because it will more than likely shock the fish. In my 20 gal I do a 25% to 30% water change weekly. I try to get the water as close to the same temp as possible and make sure its dechlorinated with water conditioner/stress-coat. I am not sure about a smaller tank, but before doing anything extreme, I would wait for an answer from one of the forum pros.
For the bettas, if you don't have a filter, you should be changing about 50% of the water twice a week. The water level is getting lower because your water is evaporating. The warmer the water, the faster it goes. I have to re-fill my tanks every 2 days because they are all at 80 degrees, and every day, about a half an inch of water is gone. Saves me from having to run the humidifier this winter though haha!
Jahjewa is right, make sure you are treating the water with a dechlorinator. I use Seachem's Prime, except when my betta was in a smaller tank, I used one for bettas because it measured by the gallon. The reason I use Prime is because it helps "get rid" of the ammonia, nitrates and nitrites, and also helps with their slime coat. And I ALWAYS make sure the water I am putting in there is the SAME temperature as the water that is in there. Also, since betta tanks are so little, I use a turkey baster to suck the junk off the bottom every single day.
Hope this helps! Good luck!
Well, I do have a filter in there, but how am I going to get the clean water at the same temp as the water already in the tank, because I have a heater in there? Do i take my betta out of the water when I do a water change?
Do you have a thermometer? If not, I got mine at a pet store for $2. The glass kind that hangs in a tank by a suction cup. I run the water in the bathtub or sink over the thermometer until it is the same temp as the tank water, then fill up my bucket. When the bucket is half filled, I put in the water conidtioner, (and I always use the amount for the whole tank), and continue filling the bucket. Take your trusty bucket of water to your tank, turn off your filter and heater, and get 50% of the water out of the betta tank (I never take my bettas out, less stress that way). Then I have a smaller container that I use to fill the tank back up, and I try to run the water down the inside walls of the tank so the betta is not getting swirled around, and pour it slowly.
Even though both my betta tanks have filters, I still change 30%-50% of their water once a week. Fresh water makes them stay healthier!
It's OK to leave the Betta in the aquarium when you do a partial water change. If you get a syphon setup from an aquarium shop, it should have a large diameter pickup end attached to a smaller diameter hose. This lets you clean the substrate without sucking out the gravel. The standard procedure is to syphon off about 25 percent of the water while cleaning about one half of the substrate. This leaves half the beneficial bacteria undisturbed. It also means that replacement water temperature is not too critical, because you're replacing a relatively small amount of water. Based on lots of water changing experience, I usually run the tap until the replacement water feels like about the right temperature. One Betta does not eat much, so if you have a filter and don't over feed, the 25 percent water change should work fine. The 50 percent water change recommendation probably started because many Betta tanks are really small and unfiltered. Replacement water temperature in that case becomes critical.
It seems like 80 degrees may be a little warm for Bettas, but if it works, fine. Prime water conditioner is also a little more serious than Stress Coat; however, it's good if you have an ammonia problem. When doing partial water changes, be sure that the syphon hose and the drain/fill bucket have no soap or chemical residues.