Natural Chemistry PhosfreeExtra Strength quickly gives you back control over pool by removing phosphates. Phosphates can get into your pool from other pool chemicals, fertilizers, sweat, and many other sources and wreak havoc on your pool. Simply add Phos Free to your pool skimmer and its unique formula coats your pool filter, which then traps and removes phosphates quickly. Best of all, PHOS Free Extra Strength is unconditionally guaranteed by Natural Chemistry to remove phosphates from your water, allowing you to buy with confidence.