In the now defunct Angelfish Web Forum, we had lots of discussions about the snails that come with most planted aquariums. Probably there is no reasonable way to exterminate them, but it is possible to control the little boogers, and it is possible that, in limited numbers, they actually benefit an aquarium. The two most effective controls that I know of are the lettuce lure and Indian almond leaves. Snails need a high pH and hard water to have healthy shells. The combination of live plants, almond leaves and Malaysian driftwood seems to lower pH and hardness. Once they're lured to their demise by the floating lettuce, the improved water conditions help keep their numbers in check. And if their shells get soft enough, some fish will dine on the things.
