I would definately have a heater on them but im in Canada,and without one my tanks drop to under 70. I ve always bred my convicts at 79-82 degrees f and always been successful
I allways use a heater for the first 2-3 spawns and then remove it.
Once they get a routine going you can't stop them.
I have 3 pairs going for the last year with no heat. House thermostat is set on 65 in the winter and 75 in the summer. So the tanks are close to that temp.
i remove my fry at one week free swimming and the grow out tanks never see heaters.