depends what type a lifalili can be keeped in a 5, i would say by it's self, as a paird, i would say a 20 would be good for almost all except for the big 3, the problem with the them is depending on the individual fish, is weahter or not they will be satisfied chasing the other fish away, or having to kill the other fish in the tank, from working with these fish for a good amount of years it goes by a fish by fish basis