New Old Newbie Here - Needs Help!

Hello to All - I'm Suzer and although I am American, I'm currently living in England. We do our fish tanks in liters over here, but I can guesstimate what the gallon size is. I have a 12-gallon tank with one Dwarf Puffer, a Sailfin Plec and a worried snail (the snail and Plec were in it before the Puffer came along and they may get rehomed). I also have my pride and joy, a new 70-gallon tank that's only been up and running for about a month, and doing very well so far. I am confused about water changes and have posted some questions on this site already. I'm trying to read as much as I can and to visit these different websites devoted to fish-keeping. Nice to meet you all at 'My Aquarium Club'.

welcome but why did you post this like 3 times? you are going to have to wait for other people to come on because im not the best at keeping track of water changes but i would say a 10-25% every like 2 weeks or something but the bigger the tank the less you have to do water changes but the smaller the tank the more you have to do water changes

Sorry, I didn't mean to post this question so many times, it's just that I put the question in general forum and then seen you had a questions area, so then posted it to questions. Apologies for the repetition!

Welcome to our forum!

The most important reason to do weekly partial water changes is the fact that an aquarium is a closed system. Fish waste, food waste and plant decay all put ammonia in the water. Even small amounts of the stuff will kill fish, but the so called good bacteria in an aquarium will break the ammonia down into food for live plants. Ammonia is a compound of nitrogen and hydrogen, and plants need nitrogen. A new aquarium needs time to grow enough good bacteria to convert the ammonia. Gravel and live plants from an established aquarium will have the bacteria and will help cycle the aquarium. The cycle, strange as it seems, is called the nitrogen cycle. To know when it's finished, you'll need an inexpensive water test kit. When the ammonia and nitrite are at zero, the water is safe.

The nitrogen cycle works up to a point. If an aquarium has a large biological load (too many fish and too much food) it will overwhelm all those good cooties and interrupt the nitrogen cycle. A small aquarium with a large biological load will need frequent partial water changes. On the other hand, I just set up two new aquariums and floated a bunch of hornwort on top. The fish are happy, and the ammonia never tested anything but zero. The aquariums are not over populated, and the fish are not over fed. A healthy fish will usually appear to be very hungry. If they don't want food, they don't feel good.

Finally, please do some research on the fish species you put into a single aquarium. I like to look at puffer fish, but they're not a very good choice for a community tank.