http://www.waterfilters.net/Pentek-PCC-1-Phosphate-Water-Filters.html
The Pentek PCC-1 Water Filter Cartridges contain food-grade hexametaphosphate crystal that dissolves slowly in water to inhibit scale and rust build-up. The water enters from slits on the bottom of the filter cartridge and works its way up the bed of media. It is recommended for use with ice machines, coffee and vending machines, food service equipment, water heaters, air conditioning equipment and many other types of water processing equipment. The PCC-1 is effective for treating scale, corrosion and iron problems for up to six months at various flow rates and feed concentrations. It keeps hardness particles separated so they cannot precipitate and form deposits when heated. It also forms a protective coating on all metal surfaces, safeguarding against acidity/alkalinity, hardness, chloride and other factors which effect the corrosion of water equipment and pipes. It works best with water having less than 15 grains of hardness, lass than 1ppm of iron, and a ph between 6.0 and 9.0.
