I have a small rhom, around 3 inches. Its housed in its own tank next to a tank containing 3 x 7 inch reds. He can see the reds through the glass and is constantly trying to break through. When I put a piece of card between the tanks, I hardly see him, he just hides behind the plants. I had a plec in the tank before he went in, which I thought would be ok, no way, he chewed it to bits. It seems to me that if he was in with the reds he would cause mayhem. If he's not afraid of fish more than twice his size, what is he afraid of, other than me? lol As someone said to me once, the only thing you can keep with rhoms is snails.