Water softener companies carry it. $15 for 40# bag, pure white 'rocks', food
safe.

Why do water softener companies have it....and why would you need that much. I
bought less than 5 pounds last year for less than $5 and I have over 15,000
gallons....I still had some left this year Jerri

http://www.fringeweb.com/Ponds/JerrisPond