Convicts are nearly indestructible. I had one live for a months on an unheadted, unfiltered tank I had in full sun on a north facing deck in late summer/autumn. He thrived, despite the regular 95% water changes straight from the hose and very irregular feeding, and grew into a fat chunky male with a nice hump on his forehead. Eventually I decided he was too nice a fish to leave outside and brought him in.
If you want a fun, newbie-proof fish then you can't go past them.
Oh, and he started out as a 1cm feeder in a tank with a black arowana, oscars, jag, and fire eel!