Carl Beyer wrote:

I sure hope this group is still alive......

My 500 gallon pond is near a sprinkling control for the house. Last
night, around 4 or 5 AM it burst, and ran city water into the pond for
about 3 hours at least.

We caught it, but my mosquito fish are all dead. The big Koi and
Chubunkin fish have been "breathing hard" since. I immediatly turned on
a water fall to aerate. But 4 hours afterward and I still have heavy
breathing fish.

I took a sample of water to the LFS and it tested fine, but I was told
to apply some water conditioner.

The LFS owner thinks I may have clorine poisoning, and that it is just
inevitable that the fish will all die within a few days...

From the line break to the pond is about 1 foot, over dirt that does not
get any poisons or fertilizer so I am pessimistic this is an issue. I
am a bit surprised about the Clorine, although it is raining in LA, as
the water was gushing out of a pipe and hitting oxygen before the pond...

I don't think it's "inevitable" but I guarantee you that it's chlorine (not
really poisoning - their gills are burned). Oxygenating city water will
not deal with chloramines. Definitely keep the water fall on, though, as
they need all the oxygen they can get right now. I'm sure you'll lose
more, but probably not all.
--
derek