One pair of brichardi will take over the whole tank if the fry are left to grow out. I had a pair of a closely related species in a 55 with other cichlids. Only about a dozen fry from the first spawn survived, but as they grew larger they helped protect the following spawns, so more and more fry were surviving each time. By the 4th spawn they had crowded the other fish into one corner, and were moved to a 38 of their own.