Bill,

That's an interesting concept...using the PTO to pump the water. Have you found a pump(s) which will accomplish that and what is the pumping rate?

As you probably know, it takes a lot of water to make a dent in the level of a sizable pond.

Depending on flow rates and the existing volume of the water in the pond, I wouldn't worry so much about the temps but would be concerned more about lack of DO in the well water. Several past posts about approaches to aerate well water before placing in pond and that should also cause some movement toward ambient temps.