Sorry to hear about your fish.
Re: adding well water; I use venturi injectors placed at the bottom of the pond to mix air with the well water. Bruce's horizontal aeration would not work for me because my water tank is gravity fed to the pond so I only get about 20 psi. The injectors work really well for my application. In the summer I run about 20 gpm overnight every other day to maintain the level.
Here is the link to the manufacturer:
http://www.mazzei.net/agriculture/index.htm
