This is great info - I've been able to find annoyingly little re. the low-temp tolerances of fish.
My silver aro will start to outgrow this wall-build by the fall (only 17" wide) so I'll be breaking ground on a pond towards the end of summer. This house is on a mountain and winter days are 24~27C if the sun is shining, but 18~21 at night Dec-Jan-Feb with occasional drops to 14~16C. Not a million-miles from NickChevy, but without the cold & hot spikes.
So 55F air-temp for an occasional overnight should be fine, particularly if >50% of the water volume is underground and I float styrofoam on the surface and/or a tarp for chilled rain. I'll ask the importer about RTC!
What other sp. should be Ok in NickChevy's pond?
According to USF&W Cichla temensis die at 15~16C, which is why they didn't "take" in Texas in the '80s; however, this wouldn't seem to jibe with Fla's winter cold-snaps nor Blakewater's experience with RTC considering they come from the same streams. My clown loaches got quiet when the office tank got down to 21C in January, but nobody else seemed to notice. They were back to full mania by 23C. If they ever get into the pond I'll have to plump a dribble from the solar... doable, totally doable.