But to the extent possible, I don't want to add heat to the pond and I don't want to exceed 85F through the depth.
So are you saying you aren't trying to cool the water but rather prevent the mixing of the warmer water at the surface until it has fallen below 85F?
Good idea but there should be a fail safe that aerates after a certain time if the condition is never met. Even up here in DFW we get night time lows higher than that.
