Quickly Reduces High Phosphate Levels Natural Chemisty PHOSfree Commercial Strength is specifically designed for a high level phosphate removal. It will help maintain low levels of phosphate. It works well on the filter. Recommended usage is 4 oz. per 8,000 gallons of pool water. This is a not toxic product and this purchase will come in a one liter bottle. Natural Chemistry provides the highest quality products to help maintain a healthy pool.