I tried the trough heater last fall and although it kept the pond clear we estimate it cost 40 bucks to keep a 2000 gallon pond open in November. It would be less if you also covered the pond.
That explains why we did not notice a bump in the electricity ... our pond is only maybe 400G ( not really sure as it is irregular in shape )
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Steve
“The most important decision you make is to be in a good mood.”
― Voltaire