in my 40 AIO cube i have 2 clowns, flame hawk, hellfrichi firefish, 3 chromis a cardinalfish and an urchin (added a week ago) thats been running for a year pretty much added in that order. My flames been in there 7 or 8 months of it... he killed my cleaner shrimp months ago but leaves all my crabs and snails alone and has never been a ****** to the fish. i feed frozen throughtout the day. i think the secret is giving them high perchs, like a hawk persay, to look out and about and keep em happy. the longer the tanks been up the better your tank will handle adding him as far as nutrients and things etc.