On 06/02/2012 17:35 harry wrote:

A pool aerator keeps it ice free for a few degrees of frost. They
often have quite a long pipe anduse much less electricity.
My koi survived last Winter no problems.

Thanks. Care to provide a name or link? Google doesn't seem to want to
throw up anything useful.

My only concern is that it would tend to turn the water over and lose
the 4ºC 'warm' layer at the bottom when the top is freezing. Is this an
issue at all?

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F