Heated Pond Winter Months In the north Anybody doing this , I would love to keep tropical fish in the freezing winter out side to get optimal growth and color , If so what size and what type of heater how Hot tub heater
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Wanting to do the same thing and I am more north than you.
I think to make it a reasonable cost, it would have to be in an insulated shed-building.
Could heat via wood boiler if your rural or solar panels - cheap.
Ideally it would be quite large to avoid fluctuations, and would want some way of chilling in thr case of a heat spell. Maybe mass water change or ground loop heat exchange.