JW here is an answer by Theo who has a similar situation but first an excllent link on the subject.

http://www.pondboss.com/ubb/ultimatebb.php?ubb=get_topic;f=20;t=001274#000000

Theo Gallus
Moderator
Member # 1187

Member Rated:
posted April 09, 2006 08:00 PM
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Eric:

I moved my Koenders' output from 7' to (2' to 3') depth this last Winter for the first time (do a search for "supercooling"). It still had plenty of lift to keep the ice off, although the hole was perhaps 2/3 the size of what it would have been in deeper water.

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Non carborundum illegitimatus!
(totus res in temperantia)