The well water enters the pond under the surface. There is a float valve hooked to a 1" water line with a nipple that in under the surface. So...it has no chance to pick up oxygen as it enters the pond.
I basically only use the aeration in the winter to keep some holes in the ice. It is an electric 1 HP motor hooked to a aeration pump. I have two stone type aeration blocks in the bottom of the pond. I will occasionally run it in the summer if the water starts getting nasty looking but have not run it this summer except for maybe a few hours once or twice.
