Bill,
A phrase I hope to never say: "Up to 20 this morning..."
Why do you turn off the aeration after you create hole?
I primarily use the aeration in the winter to keep sunlight in the pond for the DO producing vegetation. When I get real thick ice or snow cover that's blocking out the light, I blow a hole. I could probably let it run all the time as the winter diffuser is only in 3 feet of water or so but then I figure why even take the chance of super chilling the pond.
...And the best reason of all to shut it down is so the ice cover can keep the dang geese out! You would be amazed how many geese can fit in a 75 foot diameter hole when it's the only open water for miles!