I generally do water changes once a week and its normally 30-40%. I only have a 40l tank and i think it is important to keep up todate with water changes because the water quality is much harder to maintain in a small tank.
I do 10 to 20% weekly and spread the tanks out over the week, all the large ones at the weekend and the smaller ones in the evenings after work.
I dont vacume my substrate at all any more, if there is uneaten food or any large "waste" that can be seen i will net or syphon it out but other than that all that gets changed is the water and mechanical filter media.
I do weekly water changes and take out 30 percent, but it's changes from 30 to 40% I'd say. I vacume my gravel weekly too, and often change the surroundings of my tank
i do all 3 tanks weekly, 30% on my 108Ltr community tank, 50% on my 22Ltr Fry tank and 40-50% on my 180Ltr Mbuna tank. Religiously! BUCKETS BUCKETS BUCKETS BUCKETSand more BUCKETS!LOL GRJ