I've had Brazilian puffers, I think a total of 4, iirc. I believe that dwarf puffers are roughly similar in behavior and preferences. Only one would eat flake and dried food, the others would only eat frozen or fresh meaty foods. You'd probably need a large tank for the snails to breed faster than they're eaten. Imagine a bunch of little attack helicopters hovering and darting around slaughtering snails in a 24 hour/day bloodbath...