I have been keeping various tropical fish in several tanks for a year and a half now, and felt a bit more confident. I snagged a beautiful 4 inch Jack Dempsey a couple months ago and kept him in just a 10 gallon for a bit until I got my 75. He was very happy when I moved him to the big one, and with the help of the local mom and pop pet store I picked out a pink convict and a green severum. Both are about 2.5 inches. Hard to find those types of cichlids at the size to match jack dempsey, so I approached with caution. Everybody gets along with the occasional chase, but surprisingly my jack dempsey isn't the problem, the pink convict seems to dislike my green severum. I added them both in with Jack Dempsey at the same time, there is plenty of space, I have 3 caves for hideaways. Green severum has some nipped tail fins, and I frequently see him avoiding the convict, but when they end up too close the convict gives chase until he decides the severum is far enough away. He doesn't try to kill him, seems more of a territorial issue but happens all over the tank. They have been together now about 2 weeks maybe, I was waiting to see if they would establish their own spaces. Is there any amount of normal fighting amoung these types of cichlids? Also, just added a 6 inch clown knife and 3.5 inch firemouth who are adapting well into the tank. Just a mean little convict I think!