Product description Eliminates phosphates (algae's primary food source) to starve algae. Can be used all season and is perfect for pool closing in the fall to control algae during the winter months. Unlike algaecides that kill existing algae (resulting in a release of phosphates by the dying algae), PhosFree eliminates phosphates from the water to solve even the most stubborn algae problems. Weekly Dosage: 4 ounces per 8,000 gallons, (Increase dosage for excessive phosphate levels). From the Manufacturer Phosfree reduces phosphate levels in your pool. Phosphates are the limiting nutrient for algae growth. Reduce phosphates to near zero and enjoy an algae free pool. Natural Chemistry unconditionally guarantees it.