Even when I would get an order from someplace that tank raised clowns, each type would come in one bag (i.e. all percs in one bag, all tomatos in one bag). For a few weeks eveything would be fine, then they would start beating each other up. IMO, if you started with 20 clowns in that tank, you would only end up with a few pairs (4-6 clowns total). I wouldn't put more than 2 pairs in there.