i have an OB who is about 4"-5" and is the nastiest fish i ever kept... i had him in a 180 with about 40 other peacocks and dithers, and along with my polystigma they began a murdering duo .... so the poly remains in the 180 and is ok, and the OB resides in a 30 gallon all alone... i tried everything i know of to calm him down and no suck luck...