i have a 20 gallon tank full rock setup with 9 african cichlids all from lake malawi and all between 1 and 2 1/2 inches i am wondering if it is too crowded? i originally only had 4 cichlids but the dominant demosoni was picking on one in particular and after i added the the other five he has trouble bullying one to the point of death which is good but now im worried there is too many fish. like how much filtration should i use for that amount of fish?