I would go with 2 in a 5 gallon. Majority opinion from what I have seen is around 2.5 gallons per. Make sure you have a line of fake plants or something down the center to make two distinct territories as they will establish their own zones within the tank. I have heard that otos make good tankmates if you wanted to keep a couple of those in with them. African Dwarf Frogs supposedly go well with them as well.