Sorry, my bad, and still once a week is best. You can manage with every other week. Once a month you need to do a complete cleaning. The other times replace 25-50% of the water and suck the stuff on the bottom off with a syphon. And I still suggest a bottom feeder. Most importantly DO NOT over feed... Most fish can go 2 days without any ill effects without food (unless they are fry/babies).
