PATENT NUMBER: US 6387415 PATENT DATE: 20020514
A method of reducing the ability of a copper-, silver-, and/or zinc-containing biocide to stain pool surfaces...wherein the copper, silver, and/or zinc provided by the biocide is present in the pool water in an amount ranging from 0.025 ppm to 0.7 ppm, and the ratio of anionic or cationic polymeric sequestering agent to copper, silver, and/or zinc in the pool water is between 0.7:1 and 4.7:1. http://www.uspto.gov/patft/index.html jr
