I just bougth a 3 inch red devil cichlid from my LFS and they said these guy's are really mean? Mine isn't mean at all actually he/she is getting chased by the convict? It's a 55 gallon aquarium all for him/her. What size do they really start getting aggressive because, I have 220 gallon that's housed with 1 dovii,1 jag,1 buttikoferi,and 1 festae. It will be upgraded to a 340 gallon so all the fish can have room, That's why I bought the red devil cichlid, so it can get bigger, and I can put it with the bigger cichlids. My brother gave me his 55 for awhile for the devil..It needs to be meaner because if he will be housed with the bigger fish, and he isn't mean? it will get killed more than likely!