Last year I had a heater go out and didn't know about it most of the winter. It didn't have a light on it to tell me if it was working. I live in east tx and the water got down to the high 50s before I noticed and my Oscar and jack dempsey made it. I didn't even notice anything was wrong till I went to do a water change and the water felt cold. Also this year I had an outdoor pond with a few hybrid mbuna I stuck out there during the summer. Well down here it don't freeze till November or December and I forgot they where outside till a few weeks ago. Surprisingly they where just fine, even though the outside temp got below freezing a few times. I think some cichlids handle cold better than others. I had a green terror die when the temp got below 60. A man caught a huge pacu in the lake here a few years back, it looked to be a few years old. I might try one of them cold hardy geos this year and maybe a jack Dempsey and see how they do. I can always bring them in if they look bad.