Totally agree with Cecil on this one Postbeetle as usually "stress" not a kill occurs with a pond your size and 1 diffuser.(even though that is a lot of air for most diffusers)Lots of great posts on winter aeration and when in doubt for us northerners shut it off.Wait until mid April to start it back up if it warms up by then and since you may have more stressed fish consider a slow startup like 15 minutes the first day then double that each day and on day 8 you are back running 24/7 This is a conservative formula but may be a safe one for you too.I use it on startups in warm mid season installs or very mature ponds or where I might have stressed fish for any reason. Good Luck Ted