Freshwater Puffer

I'm not an expert in puffers but I would have thought that a filter rated for 20, maybe 30 galls would be OK for a single fish. As long it is cycled before the fish goes in, of course.

When you feed them snails I'd recommend removing the leftovers. My dwarf puffers tend to just bite the heads off the snails and ignore whats left in the shell.