"Timothy Tom" wrote in message
om...
Thank you all for your thoughts. The pond has always been refilled
using an auto-refill valve put in by the original landscaper who
installed the pond. The fact that fish lived in a bowl of the same
treated tap-water that is used to fill the pond suggests to me that
the problem does not lie in the municipal water source. It is
possible that it has something to do with the auto-refill I suppose.

Axolotl said:
How are you refilling the pond? If you are using the automatic re-filler
mentioned above try filling from some other source. Use the kitchen tap
and a hose. I only suggest this as your problems started when you turned
the automatic system back on.

I think Axolotl was on to something.
Not the water itself, but something in the auto-refill plumbing.
Willing to risk 1 more fish? Try filling pond from a hose?
~MattO