The first african cichlid that died on me was an acei. The aceis are probably too laid back for the red zebra and the msobo. The acei that I use to own just minded his own business and he did not bother anyone always looking afraid. Fish especially cichlids do smell fear. I suggest moving the aceis or trading for africans that can handle the aggression of your other cichlids. Or your planned addition of more cichlids will help reduce aggression to the aceis. Hope it works for u!