Ive just got a red devil for my smaller tank aswel, there also an aggressive fish. the thing with red devils is they, they really need to be on there own as they have been known to knack other red devils in with them, its not always the case, but it does happen. thats why mine is on his own, he had knacked a few red devils he was in with, and also three oscars that were almost twice his size, very cool fish though, mine is very active, as soon as i go near the tank he comes over to see me, follows me when i move, and will also come to the top of the tank at feeding time with his mouth open lol
Mine