The goldfish and snails have been doing that job for me lately. I haven't vacuumed in a week at least. But I also have a bunch of malaysian trumpet snails.
I've also got the fish across the two aquariums so that helps out. The mosquito fish, crayfish and glass shrimp are in the sump with the plants. I also keep a large mass of hydrilla in the big tank for another small school of mosquito fish. The sump kinda acts as a breeding area and the fry tend to get pumped to the big tank...where their population is held in check by the bigger fish.
I left town this last weekend and the pump line came loose, fell out and drained the sump (no problem, they are the outdoor attraction). When I got back the aquarium was really green from suspended algae but I could still see through it. Fixed the pump, scraped the glass and two hours later it was like nothing had happened. Each critter plays a role in keeping things going smoothly.
