I currently have a green severum and a gold severum in a 37 gallon tank with a parrot cichlid, but I recently bought a 40 gallon on craigslist and I was thinking about moving the severums to that tank. I was wondering if a 40 gallon would be enough room for the two severums and another "main." I was thinking about getting a green terror, but I read that those fish can be pretty aggressive. Would it be a bad idea to put a green terror in with the two severums? If so, what fish could I put in with them, other than a parrot cichlid? I haven't had any problems between the severums and the parrot, but I just wanted to set up something new.