Originally Posted by Quarter Acre
That sounds like a fun project. I would personally consider using the windmill to pump water for a water feature like a waterfall or something decorative rather than an aeration system. In my opinion, aeration should be something that is consistent, reliable, and controlled. Wind is none of that (at least not in my neck of the woods). Surely a pump could be retrofit to the base of the mill, at ground level or just below, and used to pump water from the pond to the water feature.

There are plenty of windmill pond aerator vendors out there and it would not be too hard to purchase one of their pump units and retro fit it to your old windmill.

Everything that you describe would require replacing the entire head of the windmill, which I'm trying to avoid.