It will all depend on the bigger fish. I have had a 14'' Mono in with a 6'' Ocell before. I also had a 10'' kelberi in with a 4'' orino, I always had different sized cichla in one tank (That's how I roll I guess). It will also depend how much you feed your fish. But, the main thing is the bigger fishes attitude towards tankmates. The best time to add the smaller cichla, is when you do a 50-75% water change.