So u think the rtcs would be ok in the heat but not in the cold? What if I had some industrial heating system I could guarantee the water would stay above 70-75 all the time?
I don't think an RTC can handle steady temps well above 85-88 F, especially an adult, which inhabits well-oxygenated, cool, deep river channels of Amazon where water is probably never more than 75 F. It's a deep, relatively cool water fish... even thought the climate is very hot. That's about the heat. The cold - as I suggested in that thread I linked, unless one builds a greenhouse-type structure around their pond, I don't think it is going to work. Depending on the pond size etc,. it may be a far better investement into an indoor swimming pool than heating the nature - most usually it is a game one cannot win.