Yesterday one of my aceis was dead and i get home from work today and the other one is like this. He was attacked right? No other species in the tank has signs of anything
He has either been absolutely mullered by the other fish or he has a bacterial infection, if it happened over night... its the other fish. He will probably be killed if you don't separate them.. I always found the acei to be really quiet and peaceful as mbuna went and therefore likely to be bullied if you had a tank with thugs in.
For me.... and entire tank with a 50/50 split of either Yellow or White Labs and Acei would be the most stunning!
in that size tank, with mbuna, you need a lot more fish to spread the aggression. otherwise you will get 1 or 2 particular fish dominating the entire aquarium. dont get rid of the red zebra, another will just take his place, just get more fish!