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