How big are they now? Most of my aggression did not occur until they started to mature. I had lost zero until a few of my mbuna matured. Then it was world war 3. In my new setup I have mixed peacocks, tangs, and a few haps. I have had no problems. I have lost a few mbuna in the all mbuna tank, but now it seems to be fine with ones for 1 1/2-5 inches.