Vincent,

Now that you have edited your post and added the 2 inches I would not even worry about it. At your lattitude I would not be surprised if you loose you ice with the first rain which could come as early as this week. It's long winters with lots of snow on the ice where you should be worried.

As far as a diffuser I'm not sure you even need one there for winter, but if you do set one up in the future for winter, I would set one up on a shallow edge so as not to mix the water column too much and run only about 6 hours per day. (But with this large a pond it may be difficult to mix the water column too much anyway) Bill Cody should chime in on this one.

As far as summer bottom aeration with a 5 acre pond I would think you would need several diffusers and the size compressor and electricity you need could get expensive.

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