Is he OB bigger than the other fish? And what do you have for hidding places and things to break line of sight? If there isn't anywhere for your fish to hide once and a while they will be stressed and may take it out on their tank mates. Plus if they are getting chased they need to be able to dodge through something to momentarily break line of sight with the aggressor. This will help slow the roll a bit on the agro fish and everyone is better off for it.
I have a lot of space and caves for all of them but the OBs r staying to them self but they are taking over one side of the tank and my mbuna omg he bulling everyone