It seems like I've recently been seeing a lot of people coming to the forum site with questions regarding water changes or they have done 100% water changes only to see their Bettas not do very well. Here is some info that all should read and follow. There is also some other extra info that you might find interesting.
First of all, for every Betta it is recommended that they have
at least 2 gallons to live a happy and healthy life. You may also go up to 10 gallons for one Betta and they won't argue with you! Keeping a Betta is a bowl is not a good idea for several reasons two of which are not being able to put a filter in most bowls or a heater which Bettas require especially if you live someplace chilly. Bettas like a bit of space to swim around in and also places to expore or hide in. Bowls don't really give them those options. It's better to buy even a small tank that has a filter and put a heater in it too. Some of my Bettas are in tanks that are 2.5 gallons, 6 gallons, or 10 gallons and all of them are happy. Each of those tanks has a filter and when winter comes I'll have to put the heaters back in. Bettas like their water to be around 78-82 degrees F which will bring out the most activity in them. While they can live in water that is cooler than that, it really isn't as healthy for them and leaves them a bit more vulnerable to disease.
As for the water changes, it is NEVER recommened by a knowledgeable Betta keeper/breeder to do a 100% water change! Some pet shop employees will tell folks to do this but don't realize the harm that it causes. The problem with doing a 100% water change is that you are only dumping any and all beneficial bacteria down the drain as well as stressing out your fish. Tanks over time will grow bacteria that help keep ammonia and nitrIte levels low and safe so avoid doing the 100% water changes!
If you DO NOT have a filter in your tank, it's recommended to change 75%-85% of the water once or twice a week but no more. Some folks have said that they did a 100% water change to get rid of the poo but instead of doing that, buy a gravel vaccum! It works better than a 100% water change!
If you do HAVE a filter, change 25%-50% of the water each week. New tanks will often get high levels of ammonia and nitrItes in them which are the products of waste and leftover food. Both of those should have levels no higher than 0. Do a 25% water change if they are higher than that and be sure to remove any food that your fish don't eat when you feed them. Another thing that will help with new tanks or even established tanks is
adding a bit of JAVA MOSS. Java Moss acts like a natural filter in that it lives off of your fish's pee and poo and will help keep ammonia and nitrIte levels lower. Most local shops don't stock this (I don't know why), so you can purchase a chunk of it online at Aquarium Garden. Once on their site, search for "Java Moss" and it will take you directly to where you can purchase it. Remember, too, that using live plants also helps keep nitrIte levels lower since it removes many nitrItes from the water. Water Wisteria is helpful if you are having problems with algae, too.
If you have been doing 100% water changes, don't panic! Just start doing the smaller changes and things will quickly improve for your Betta. Hint: If you see your Betta gasping at the top of the tank a day or so after doing a 100% water change, it's probably because the ammonia and nitrIte levels have spiked. Do a 25% water change and this should help. Also, Bettas are fish that have a labyrinth organ that requires them to breath air at the surface of the tank from time to time. This is how they will build bubble nests, too. As long as there is no gasping, Bettas going to the surface for a bit of "fresh air" is normal.
Hope this helps! Please let me know if you have any questions regarding this issue or any others and I'll be happy to help! Good luck with all your Betta friends!!
