Hi All New Here.
I would recommed the demasoni, this guy stays small and is a blast to watch. I had one in a tank but he recently died so i am looking for another. (He got cought between a rock and the filter, set up a hospital tank but he didn't make it)
The Demasoni was one of my favourite fish, he was quick so i didn't have to worry about him with the other fish in the tank eating him, and he is a dwarf cichlid so stay between 2 - 3 inches long.
Another thing, with a 30 Gallon, I would stock about 7-8 fish in there. Let me know what you are thinking of doing and I can tell you if it will be compatible together. With the Yellow lab in there your probably gonna have a pretty docile tank.