Natural Chemistry® 75320 3L Phosfree® Reducing phosphate levels in pools is easy with Natural Chemistrys patented Phosfree technology. Phosfree is formulated from lanthanum (rare earth) compounds. When added to the skimmer, a thin coating of Phosfree forms on the filter media. As pool water flows through the filter, phosphates are reduced to a very low level.