I have 3 black aro's in the same tank. they have been with each other except for a couple of weeks when they were still about 4"[now all are over 2']. When I put them back in the same tank I added one floating driftwood log to ease the line of site agression. Now the floating driftwood is not in the tank and they get along for the most part,there is still some nipping from time to time but not enough to damage fins.