IF you want a breeding pair of convicts you wont' be able to keep any other fish in there with them with that size of tank. They are SUPER aggressive when breeding and will attack the other fish and kill them from stress or aggression. Convicts really just aren't good community fish unless kept as a single with other aggresssive cichlids or in a large enough tank that they can claim an area and the other fish can escape harm. Convicts do breed like rabbits. You will have sooo many babies if you do get a pair. You will know when they have paired off because they will be act as a team and defend their "spot" and terrorize the rest of the fish. but be prepared for babies and lots of them, YOu'll have to find them all homes, most
LFS wont' pay for them since they breed so easy. Convicts are a very cool fish and in my opinion very beautiful but they can be tricky since they are so darn aggressive and prolific.