Asked October 06, 2014, 8:59 AM EDT
Polk County Wisconsin
There are 3 ways often employed to keep a section of open water over ponds during cold winter: air circulation, water circulation and heaters.
There is quite a bit of information on this available on the web (e.g. google “de-icing koi ponds”) Here is one example: http://www.drsfostersmith.com/pic/article.cfm?articleid=626
Also couple of Youtube videos:
Small floating pond de-icers are the least expensive ($40+),
They only provide a small round window however, and some comments suggest they
might not be sufficient in frigid temps.
The picture on Stoney Creek’s
website provides an example. http://www.stoneycreekequip.com/form/deice.htm
With techniques described in the second Youtube video this may be adequate.
Water pumps and aerators designed specifically for fish ponds start at about $300 and go up.
Pentair Aquatic Ecosystems has an aerator unit for small
ponds for $350:
Kasco Marine carries fairly heavy duty products
All the above suppliers have reportedly good tech service people to help make a good selection for your need.