JW - nice to here from another Minnesotan. What area of the state are you in? I'm north of the Twin Cities about 50 miles. I'm new to the pond thing too (4 years) so don't usually have much to contribute. I understand that supercooling can be an issue so from the start I have only run my aerator for 2 four hour shifts each day. I do one shift starting at midnight and the other starting at noon. I have measured water temps during the winter and they drop fast if you keep the air going. My pond is only 1/2 acre mostly 6 foot deep with an 8 foot hole. I leave the air stones at the bottom of the 8 foot hole. Its easier to just shorten the aerator time than move the stones. I have never lost very many fish, most was 4 this past winter. I keep the snow off by plowing the pond during the winter with a small tractor. My pond is long and narrow so I plow both ends never getting very close to the open water. My aeration schedule keeps about a 10 foot opening most of the winter. If it stays below zero for a while the opening shrinks to nothing more than a small hole big enough to let the air out. When its really cold I go out occasionally with the rifle and have to poke a hole above the aerator. I too have found times where I just can't find the fish during the winter. I've even tried drilling many holes and looking with a camera but rarely see any. Most often they are as far from the aerator as they can get. That ought to tell us something. Right now my BG are beginning to take pellets really hard. They'll grow like crazy over the next month. Went out today and caught a number fish in the 9 to 10 inch range, they will weigh almost a pound.
