I stopped my aeration system this year once the outside air temps were consistently lower than the pond water temps. Why cool the pond down faster than necessary? I measure my pond water at the surface, 18" down and at the bottom (7' down) and using the 18" and/or 7 foot down readings are more consistent, hence a better number to rely on when comparing to the outside air temps.
I will turn on one shallow diffuser if/when we get the threat of ice over, but only for the duration of the threat. We don't see a lot of ice here, if we do, it last for a few weeks max.
