your tank is ok for a single convict but as for tankmates, i think thats about it sorry. its not so much there size just their territorial issues have you considered a more peacful fish like rams or keyhole cichlids?
Dan
Convicts are tempermental. Some can't live with others and some can. A femal con or two might do ok with some other fish.
I have two males in my 40 gal, but they were born and raised in the tank and all the other fish were there before them. With that said, i never notice any aggression from them towards the barbs or tetras and danios in the tank.