Assuming you keep your africans in an all african tank, just move all the rocks and stuff. This tends to kill their hyperdominant attitudes. They have to restructure their social pyramid avertiem there home is distrubed. Do it a few times in a month and the bully becomes the bully sometimes. Keep 150g of africans, my south american tank is unused ATM. Also, do not overstock africans. I keep about 13 fish in my 150.