here is a cool article: http://badmanstropicalfish.com/afcichlids_setup.html

and a quote of what we were trying to do
" Also, by "overstocking" your tank, you can distribute inter-species aggression. Not just one fish is a target of abuse, and aggressors tend to lose victims more easily when the tank is crowded. Just be sure that you "over filter" your aquarium if you are going to "overstock it."