sorry to hear this mt......if you didnt know it before, you will know it now, and that is that typical groundwater is depleted in oxygen. when you pump water directly from a well and deliver it to pond w/ no aeration in between you can suffocate yer fish if enough volume is mixed w/ the pond. sounds like you put alot in almost half the pond volume. one idea could be to run that well water down a say 25 to 50 foot rip rap path to the pond. this gives the water a turbulent oxygenating ride from the pipe to the pond. good luck down there.....

GSF are people too!