I had seven (7) in a 150 gallon FOWLR. They didn't exactly get added at the same time, but were mostly the same size. Of course, one or two will always be the 'runts', and they preferred the far end of the tank, near there own rock. At least they didn't quite ack like Chromis-- picking each other off one by one. However, the coukd pick up some lightning speed when spooked, and more than one time they seemed to scrape an eye on a rock, which took much time to clear up. I have heard others mention this about Chalk Bass.