some of them get 40-70% a week
some get 20% every other week
one 40% every other week
one gets 50% every few months
one only gets topoffs and has never gotten a change
30% every week. or the week following my last WC i'll clean my AC110. i never touch my eheims. last time i cleaned em out my tank when through a crzy mini cycle.
I think it depends what you have in your tank. If its overstocked, then larger and more frequent. Normally, I guess its 25% weekly. If there is something going on like algae boom or a disease, thats the only time I got 50% on that weeks WC. I dunno everyone has their methods.