Pro Series® Extra Strength Clarifier™ 20311PRO 1 gal . PRO SERIES® Extra Strength Clarifier is a clarifier made from the recycled shells of crabs and various sea life. Crabs and other crustaceans have a product in their shells called chitosan that attracts small particles of debris in water. Use to effectively and quickly clear problem water or to polish dull water by removing small suspended particles. PRO SERIES® Extra Strength Clarifier is compatible with all sanitizing systems and can be used at the same time as shocking pool water. It also improves filtration.