What you say about agitation does make sense to me, but what I wrote is the advice I've read many times on a pond forum I belong to. I'm not sure then why so many folks from that forum do it that way.
Some members there don't use their air stones at all, but instead use a "pond breather" during the winter months stating that it is far superior to using air stones. With a pond breather you don't have to worry about keeping a hole in the ice. The pond can freeze over completely, and a pond breather still releases the toxic gases.
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