The use of aluminum sulfate (alum) coagulation prior to reverse osmosis (RO) treatment has been shown to be problematic. Membrane fouling was theorized to occur through soluble aluminum (Al 3+ ) reacting with ambient silica (H4SiO2) to form kaolinite (Al2Si2O5(OH)4) within the RO unit. Chelating agents (citrate at 34 mg/L and ethylenediaminetetraacetic acid [EDTA] at 16 mg/L) were tested for their efficacy in controlling aluminum silicate fouling. The results of bench-scale testing demonstrated that both citrate and EDTA did control aluminum silicate formation, citrate more so than EDTA. Additional aluminum-based fouling was encountered when a commercial, phosphonate-based antiscalant--used to control barium sulfate scaling--reacted with the excess aluminum despite the presence of either citrate or EDTA. Includes 30 references, tables, figures.