its the same with any other "rule" of fish keeping. its application really depends on too many factors to be the same for everyone.
general rule of thumb is 25-30% weekly. this includes vacuuming, etc.
overstocked tanks, or tanks with messy fish like plecos, goldfish, oscars, etc. will produce a higher bioload, which would require more frequent or larger changes. while planted tanks can get away with less because of the additional "filtration" the plants do.
so it depends on the tank. but you cant go wrong sticking to 25-30% weekly.
A forum community dedicated to Aquarium owners and enthusiasts. Come join the discussion about collections, displays, product reviews, accessories, classifieds, breeding, health, behavior, housing, care, and more!