Depends what you want to do with them. If you're wanting to breed, try 1 male and several females. You'll get alot of fighting with more than 1 male in small groups. A larger group of say 8 to 10 with equal amounts of males and females would probably work because of the crowding, sort of like the pet shops. Remember, these guys like to dig large nests, so provide lots of gravel. And, keep up those water changes.