the air temp is going to determine how deep the frost is going into the ground.
everyone in the "north" depend to a very great extent on the warm earth (55o) keeping
the water liquid. if the frost goes lower than the depth of the pond it is going to
be like trying to keep an above ground pond thawed. bocu electrical bills. Ingrid

I hate to sound stupid (although I'm getting used to it in my old age!), but
if your pond is only 18" deep, I would think that *air* temperature is a lot
more important than the depth of the frost line?


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