In a final effort to get the yellow out of my water, I tried a third brand of sequestrant/chelating agent, Sequa-Sol It worked. The water is the best looking it has been to date. The previous two were Metal Free and Sea Klear Metal Klear. The MSDS on this new one says the active ingredient is Sodium Citrate. It is listed as a chelating agent where the previous two used Acrylamide-Acrylic Acid Copolymer, listed as a sequestrant. I can't find much that explains the difference, at least as it pertains to pools. I am trying to understand why this worked and the metal free that worked last year didn't this year. Does groundwater change that much year to year?