Wow winter just arrived this week in my part of the world. However that is not to say that we wont see temperatures back up in the 60s and even 70s next week. It is the fluctuation in temperature at this time of year that can cause problems in your pond.
If you have a very deep pond the temperature fluctuations will not be as dramatic. However in a shallow pond it can be substantial and this can stress your pond life. Stressed fish often get sick or even in worse case scenarios die. What a pond owner therefore wants to do is try to stabilize the temperature of their pond so it doesn’t fluctuate as much and doesn’t have vast variations in temperature through the pond.
An air pump can help with water circulation that will ensure that your pond water temperature is more consistent throughout the pond. Also as long as the pump is insulated it will pump air into the pond that is not too cold. It will also keep a hole in the ice to ensure that gases that are detrimental to your fish can escape.