[prairiepanda]

I would think they'll get eaten before their poop starts to become a problem. Once they're gone, however, I would suggest switching to something else. My crayfish lived with a wide variety of other critters that I had caught from the same location(I attempted to replicate the aquatic ecosystem from that location as closely as possible) and everything stayed in balance quite nicely except for the fish. Everything ate the fish. Even the fish ate each other. Eventually I gave up on re-stocking the fish and replaced them with salmon pellets, which all the fish-eaters happily ate. Just one little minnow survived the entire time I had the tank going.