how often do u do a water change in a freshwater fish tank

A 20% water change once a week is what I do...

20% once a week (usually every monday or tuesday) is what I do aswell. I prep the water 2 days before so everythings ready to go when i need it. :)

For me it depends on what is going on with my tank at the moment. Some things that may affect my water changes are 1) whether I've been using medication(s), 2) if I have especially messy fish, 3) if I have more bottom-feeders, 4) my water parameters, 5) what type of filter and especially what type of filter media I'm using, 6) whether I've fed messy food lately, 7) if I have new fish, 8) if I have easy-stress fish, 8) if I have pH sensitive fish.....well, I guess you get the picture. LOL

And after having said all that, I do generally agree with a weekly change. I try to do smaller amounts more frequently because my tap pH is about 8.2 and I use driftwood to bring it down. If I pour in a ton of water the pH shoots up until the driftwood has a chance to do its magic. If I'm not careful, my tank can go from 7.8 pH to 8.2 pH in minutes. Yikes!

Zambize