Buffer - I never say never when dealing with pond problems. Your situation is more complex than most. Your pond could winterkill given the right or wrong conditions. Firstly, does the pond have tannin stained water? This reduces overall productivity, affects phytoplankton quality and natural oxygenation. Is the water clear even with some stain or is it fairly turbid? do you have any water clarity measurements? High amounts of organics (submerged vegetation, tree leaves?) in a real old pond with quite a bit of noxious, anoxic decompostional gasses, water clarity, an incomplete destratification in late fall and lack of sunlight from late Nov to April, could all combine into a winterkill. Some small deep ponds are not holomictic (complete circulation), nor dimitic(bi-annual mixing). Late fall and/or winter plankton blooms could also play a role here. Stratification cycle of your pond is important to know. Does the pond get enough winter winds to blow large patches of snow off the ice? Depth is not the main factor for preventing winterkill, although it does play a very important role.
I will assume that you do not live at the pond. Regular snow removal will pretty much eliminate the chance of winterkill in your far north, deep pond. A few of our members from north central Canada regularly remove lots of snow from their ponds in winter with up to 36" of ice and fish (trout, etc) survive winter okay.
IMO your pond is too large for one windmill to be real effective at preventing winterkill, although if the conditions are marginal a windmill might help prevent or reduce a mild winterkill. Not all winters are alike. Definately two windmills would be better than one in a large 5 ac pond. At this point I am not positive about placement of the diffusers of 1 or 2 windmills. It would depend on the style of windmill and stratification features of the pond. Some windmills produce more air volume and better pressure than others. If your pond is truly 37 ft deep by recent actual measurement, then it will require 18-20 psi to release air at that depth. A real challenge for any windmill. It takes a pretty strong wind for a windmill to generate 18-20 psi. A light or moderate wind speed will definately not do it, thus your bubbling and mixing times will be noticably reduced compared to a windmill 'working' in a shallow (8-13ft deep) pond.
Presence of chubs and suckers suggest that the pond has a small feeder stream? Suckers and chubs normally will not spawn successfully in 'true' pond conditions, i.e. no moving water. I assume you can tell the difference between bluntnose minnows and suckers; both look quite similar. bluntnose and redbelly dace spawn in ponds. Maybe some close-up photos of the small fish next summer? Given perfect conditions creek chubs could spawn in ponds but it would be extremely rare. Most chub species spawn in similar conditions to trout utilizing redds in stream beds.
This link to our Achives may provide helpful info for posting pictures. Ask if you have questions or problems with this. I am not a 'big' picture poster, but there are numerous others here that can provide lots of good advice.
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=92443#Post92443
