I have a 55 gallon tank, I have 9 fish in it only one of them are a very big bioload hes a fantail goldfish. So I normally do a 25% water change once a week then every two weeks do two 25%. My other 20 gallon has 3 guppies I do 25%-50% every week on it. Should I be doing anything different? I haven't had any issues with my water but I was wondering what everyone else does?