Do give Dwarf Puffers a try - they are some of the most interesting FW fish and they really do need a species tank. 4-5 in 20 long would be about right. Do go heavy on hardscape and plants so that they can establish their small territories.
Be prepared to feed them live snails and blackworms. They should also take frozen bloodworms.
v3
Be prepared to feed them live snails and blackworms. They should also take frozen bloodworms.
v3