It depends on the species. Some of the really small ones, maybe, but a 20 isn't a lot of room for them to establish separate territories if they don't get along.franchise513;2215292; said:alright thanks guys and i like the idea of 8 or so school fish like the cardinals with 6 or so cories and a main centerpiece like a gourami, could i put like 2 gouramis in the tank, like two different species?