I'm sure this won't work with all convicts, and I'm suprised it does with mine, but I have a 20 long with one full grown male convict and a yoyo loach and a kuhli loach. The kuhli isn't that interesting to me since the tank is soo full of hiding places that I didn't even know he was still there until I did a full tank renovation this summer and found him. I was pleasently suprised since I've had him basically since I started keeping fish. But the yoyo and the convict are really nteresting to watch together since the yoyo will sneak up on the con, suprise him, and then swim back as quick as he can to his side of the tank, and it just happens over and over. The convict hasn't touched him yet, but he did kill the 2 other yoyos I had. I love that con because he's huge and almost black and nearly jumps out of the water whenever I try to feed him. He has a ton of personality. I have a breeding pair of cons too, but I kind of hate it. the fry simply do not die and are hard to get rid of. The adult male is fun tho cause when you put your finger next to the tank you can here him bite the tank.
They're cool fish...I guess...I'd suggest something like firemouths though. I like plenty of other cichlids better, just cons are the ones I'm stuck with.