They are partly correct.. if not dosed correctly (ie not accurately knowing
the gallons of water you are adding it to), PP can easily cause gill damage,
which may not be immediately apparent, but will be permanent...
This is not immediately apparent with younger fish (with smaller body
surface areas.. unless they were really overdosed, in which case they will
die), but as the Koi/GF get large, they aren't able to supply all the oxygen
their tissues need, based on the PP induced gill damage. Then all it takes
is a little stress by things like high water temp (low oxygen), or long
winters, etc, and you will find they die, while the younger fish seem to
survive, and no one seems to know why!
Now you know one cause of death of the larger fish, when the smaller seem
ok.. previous gill damage (which may have occurred long before you received
the fish).
PP is perfectly safe to use, as long as you have an accurate measure of the
gallons of water you are introducing it into.
Happy ponding,
Greg


"Keith and Wendy Slonecker" wrote in message
...
I got my PP at the Culligan water treatment company in our area. they
have
a website at www.culligan.com where you can find a store near you. I
think
I paid about $36 for the only size they had which was about a quart.....
plenty for many years.....

by the way, they thought I was crazy when I told them what I wanted it
for,
my pond......... if I had to do it again, I would not tell them what I
wanted it for at all! they said I was going to kill all my fish and that
I
was mis-informed........ nice thing was I could pick it right up and not
have to pay shipping costs.

just my 2 cents.

wendy in Oregon