Greg Cooper wrote:

A quick Google on evaporative cooling turned up the following.

http://www.consumerenergycenter.org/...e_coolers.html

It states that evaporative cools in dry atmospher can cool the hot air
by as much as 30 degrees. The plus is that they use much less engery
that a AC unit.

It would seem one would need a evaporative cooler to chill air then an
air/water heat exchanger to cool the pond water. It sounds doable.

Not necessarily. Any fountain is going to work as an evaporative cooling
mechanism - the finer the spray the more effective (but also, the more
water the pond loses by both evaporation and wind-drift).

If those aluminum radiator coils were buried somewhere cool, you'd have a
heat exchanger, and it would be effective. The challenge will be that the
ground gets pretty hot in AZ in summer. So finding that cool spot will be
work, and the digging will be deep.

Again, that's for a "perfect" solution, but you don't need refrigeration,
just enough cooling to keep the pond at a nice temperature. I don't know
Arizona, but you only need to be down a couple of feet to be significantly
cooler than daytime air. Basically, if you can get the heat exchanger into
any soil that stays under 80F, you should be cooling the water below the
danger zone for your fish.
--
derek