I'm aware of heat pumps which use the earth as a heat sink, usually
via a burried pipe. Your scheme should work, but will be less
effective due to entropy.

My BIG question is "Why? Are the fish dying due to temperature
changes? Fish are cold blooded creatures (just like politicians) and
the water itself should be providing a sufficient buffer against too
rapid temperature changes.

PlainBill

On Fri, 03 Nov 2006 13:44:43 GMT, Peter Breed
wrote:

I have a relatively small pond of 2000L or 550 UsG, and one the problems
I have is fairly large swings in temperature. I was considering using
the heat of the ground to moderate long and short term temperature
fluctuations by burying a pipe 3 feet or so underground round my garden,
and pumping the pond water through.
The idea came from methods for heating and cooling houses by a similar
method. I've tried a few web searches but not found anything relevant
yet. Has anyone come across such a scheme?

Peter