Coagulation optimization using coagulants of ferric chloride (FeCl), polyaluminum chloride (PACl), and their combinations (FeCl/PACl) were evaluated through jar tests, by treating source water with high algal content (10-40 million cells/L) and high alkalinity (80-110 mg/L). The results indicated that when compared to single coagulants, the combined coagulants showed a superior coagulation performance in terms of turbidity, UV and algal removal. The optimal dosage was determined as 30-35 mg/L by using the combined PACl/FeCl (1:2 by mass) and dosing PACl followed by FeCl. By adding the coagulant aids of polymerized diallyl dimethyl ammonium chloride (HCA) and polyacrylamide (FO4190), the floc sizes may enlarge up to 1.75-2.0 mm. Scanning electron micrographs showed that the coagulant combination can form a more compact reticular aluminum-ferric structure, and thus increased the settleability of the flocs. The combined coagulation was further evaluated in full-scale water treatment plants, confirming the improvement of the removal of algae, turbidity, and residual iron in the treated water. © 2013 Copyright Balaban Desalination Publications.