Another idea if it is a freshwater tank is a crayfish. They come in all sorts of neat colors and love to munch down on any snail they come upon. The only concern with this method is they are mean to fish that stay close to the bottom of the tank. But if your tank can handle a crayfish, considering they can get up to 8inches in some breeds, go for it. I had two for awhile one in a cool water tank and one in a warm water tank, i had to trade them eventualy because they became to aggressive with my fish that liked the bottom of the tank.