formerly know as Zero-Phos is perfect for those stubborn algae problems that no matter what you do the algae keeps coming back. Algae is a plant life and phosphates are fertilizers, they feed the algae and your pool becomes an all you eat buffet for algae. Phosphate Remover will take the buffet away. Make sure you brush the walls, vacuum the pool and then shock the pool. Next day add the proper amount of phosphate remover based how many gallons of water are in the pool and your phosphate level. 1 quart removes up to 1000ppb in 20,000 gallons of water.