I believe I have a serious water quality problem, and it is causing some of
my fish to die, 14 in the last few days: here is the problem:

I have a 3,500 gall pond, stocked with about 70 fish of varying sizes (3" to
26"). Almost all the fish are huddled at the bottom of the pond in one area,
and they are slowly dieing with a range of diseases.

I have checked the water quality and here are the results: PH 9.5, Ammonia
0, Nitrite 0, Nitrate 0, Temp 5C. I have a very good filtration system
running, which does a complete water change every 3 hours. Water is crystal
clear. There is some algae bloom on the surface, which is unusual at this
time of year.

Now I believe that my problem is caused by the low temp coupled with the
high PH is causing some kind of ammonia poisoning even though the reading is
low.

What do others think and if it is a PH problem, how to I reduce it?

Pete