I would have asked in the RTC thread, but it seems as though it is not answered very much. I am from bham, al and my buddy has a very large pond in his front yard, and he is wanting an RTC to go in it, maybe 2 (This is a man made pond like something you would fish out of and its fed from a natural spring from up the road). My question is what is the lowest temperature that an RTC can handle? He was thinking about figuring out a way to heat it but have not come up with an efficient way yet. He was thinking heating coils, but I don't know how expensive it would be its thousands of gallons of water. It has normal pond fish in it like large mouth bass, bluegill, shell cracker that sort of thing. I was telling him that they would probably not be able to survive in that, what do you guys think?