A point about the use of aeration in winter.
If the pond has had a chance to stratify placing an aerator in the pond can have the opposite effect of what is known as reverse aeration.
This likely will not affect those in states where there is little ice.
But with a pond with heavy weed growth or a significant algae bloom snow on the ice will stop light penetration causing plants to die.
As the plants die there is a buildup of gases carbon dioxide, hydrogen sulfide, sulfur dioxide, and methane. All of which are will settle to the bottom of the pond slowly building up from the deepest areas until eventually it reaches the entire pond. Winter kill or winter anoxia.
Placing a diffuser in the deep area of a pond after this has begun can circulate these gases throughout the pond and accelerate the anoxic conditions.
If you plan to use aeration start it early or in shallower water to reduce this risk. You can alway move the diffuser deeper after the pond has opened up if you feel it is necessary.
http://files.dnr.state.mn.us/publications/fisheries/investigational_reports/547.pdfWhile this was not a particularly successful experiment it will kill many game fish.
