Never really thought of this.. but when my fish had ich i used to do a water change every other day, then every three days.. And i guess i kept doing em..c.c; How often are you supposed to change your water? and how much should you change. Ive got a slightly overloaded ten gallon, so i guess it might be better to keep doing the water changes.. Anyways! How often should you do water changes and how much shouldyou change.