It was a few years ago since I had fish, but the tank had 20 convicts in it and up to several hundred fry, convicts are like rabbits.
The flatheads left each other alone and the cichlids alone, my convicts were 3" in size the flatheads were maybe a skinny 2" Had them together for over a year when one day I came home from long weekend and all my fish were floating upside down. No one else was home that weekend and none of the clocks were blinking so I am clueless how the fish died. I always check the various chemical levels of the water, etc.
I cleaned up the tank, threw away all the rocks, dead fish, heater and filter. Bought all new stuff except for tank and hood, filled the tank up, waited a month and go some new fish (no cichlids, silver dollars, tetras and other weenie fish), I had them for 9 months and needed to move across the state for a job so I gave my fish to a 5th grade classroom who lost their last fish to old age and the tank and accessories to a friend of mine.
Charby