You only need to keep a hole open in the surface of the ice for gas
exchange, allowing toxic gasses to escape and oxygen to enter. An aquarium
air pump with an air stone will keep the surface moving enough to prevent
freezing in many ponds, and they are much cheaper to operate than the
heaters. The stock tank heaters are useful, but to limit electrical usage,
only plug them in as the pond really starts to freeze over. They have a
thermostat that comes on when the temperature gets near freezing, but the
small size of heater, and relatively large open pond makes them energy hogs
trying to heat the pond, when they can only keep a hole open.
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RichToyBox
http://www.geocities.com/richtoybox/pondintro.html


"John Burton" wrote in message
...
We had a good freeze last week, ended up with ice across my entire pond
except 1) where the water falls from the bio filter and 2) the skimmer.

Question is this. In order to be prepared for the next freeze (spring
ain't
here yet) I'm wondering what type of heater (or bubbler) I should install.
Y'see I have an 11' x 16' pond, about 24" deep at the deep end. Seven
Comets and one Koi in the pond as of last spring, but I haven't seen them
for nearly two months. I expect they're hiding in the hidey holes built
by
all the rocks that line the pond.

Suggestions?

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john burton
Bach 50B3
Bass Trombone, Charleston NeoPhonic Orchestra
South Charleston, West Virginia