Brian,

1/2 horsepower it way to big for a pond your size at least in winter. In summer it won't hurt anything (except higher electricity bill than necessary) but in winter there is too much mixing even if it is off to the side. You were mixing and chilling the water this winter too much! I don't know who sized your compressor, but they either didn't know what they were doing or wanted to sell you more than you needed for more profit.

I will say it again. You need to run less air into water on one side that is under 6 feet. My .8 cfm still mixes better than I would like as it drops temps in the deeper water 2 degrees more than I would like. And thats a long ways from the center. You would be surprised as how far an underwater current can go.

As far as Russ' question about the tubing system I have a separate weighted airling and rubber diffuser set up for winter, and simply change the compressor, duck tape the ends of the summer airlines and hook up the winter airline to the small compressor. That way I don't have to move diffusers around which is a pain, and I don't kick up any possible hydrogen sulfide on the bottom which can be very toxic to fish.

Brian, I would guess anything your fish were stressed. Your larger fish will succumb first i.e your bass and larger bluegills.

If pigs could fly bacon would be harder to come by and there would be a lot of damaged trees.