There are a number of chemical reagents that are available for treating turbidity. Reagents that are available for treating turbidity include aluminium sulfate or alum (Al 2 (SO 4) 3 ·nH 2 O), ferric chloride (FeCl 3), gypsum (CaSO 4 ·2H 2 O), poly- aluminium chloride, long chain acrylamide -based polymers and numerous proprietary reagents. The water chemistry must be carefully considered when chemical dosing as some reagents, such as alum, will alter the pH of the water.