I have a tank full of guppies, 3 small snails, and a pleco. I clean the tank maybe once every six months. I pour in spring water about once a week to compensate for evaporation. As long as the guppies are not being overfed, I do not need to clean the tank. I have a very good filtration system. As long as the guppies are reproducing well, then I know my tank conditions are good. I think it comes down to feeding, pooping, and the amount and type of fish. My water is always crystal clear too.
I used to be an avid tank cleaner, but when I switched to these fish in the set-up I have, I just didn't need to be that avid tank cleaner anymore.