You can put about 3 or 4 dwarf puffers in a 10 gallon, I'm not sure if there are any other kinds small enough. You need good filtration and lots of hiding places to break up the line of sight so they don't attack each other. Dwarf puffers are 100% freshwater. You need to feed puffers snails everyso often to keep their beaks trimmed down, mine also enjoy brine shrimp and blood worms.