From what I understand you can add many clowns, as long as they are all juveniles from the same clutch, then natures hierarchy within the clan will take over, with a breeding female and breeding Male and the rest stay juveniles. I'm not sure on all the facts, but troubles can occur when they split off in a larger tank, and in turn break away as 2 families. Or they can kill off the weaker ones. Also Marc has his 60 gal nem tank with lots of clowns.