I used my ice spud to chip a hole through 12" of ice. After 4"-5" I hit a water layer and had to chip out the remaining hole in watery slush. It took 2.5 minutes.
From the temperature data so far, it appears diffusers, even in shallow near shore water, will mix and circulate super cooled water for long distances and into deep water of the pond basin.
I think CB1 is correct. Fish near the ice cover mid to late winter is a sign the DO is absent in the deep water. DO is lost first at the bottom and is then consumed toward the surface, thus forcing fish higher and higher toward the top to find acceptable oxygen concentrations. Without light getting through the ice the water directly below the ice soon also looses it's DO and winterkill occurs.
I'm going to dig out the vexilar and see if I can mark fish. On second thought no I'm not. I'd have to spent another 25 minutes boring a hole!
OTOH I suppose I could reopen the hole I made today with my spud!
