I would start with a female convict. If you dont want to put up with the breeding, get a pleco. When I got my 29g tank I put in a pair of cons and they are great to watch. Very active and interesting. When my male was close to killing my female I added a yellow lab as a quick fix. It did the trick and the 3 fish do very well together. I dont know what I'll do when the lab grows up, however.