I have a fresh water 29 gallon tank. Every 6 months or so I end up doing a complete water change and gravel change do to the pond snails taking over my tank. I have no snails for about 3 months then all of the sudden they show up again. How do I keep them from coming back? I have tried snail begone and that worked for about 2 months now the stupid snails are back again.:eeg: Can some one help me please?