I had kept mine in a tank with lots of other Fish including Cichlids , like Oscars , Jag' , Black Belt Cichlid , Silver Awo' , RTGG , Common Pleco Ect . But as soon as the Red Devil hit about 7 - 8Inch i had to split it from the group as he was just picking on and bullying them all day long . The only tank mates i could put in wiith my Red Devil was 2 12Inch+ Common Pleco but they still got pick on but not as much .
with Dovii Kid. In the 55 you're not likely to be able to keep anything else. Once you get the 225 though you'll have better odds.