The influence of anion specificity on the faradaic efficiency relative to aluminum oxidation during electrocoagulation has been reported. While with chaotrope anions, the faradaic efficiency is higher than 1, it is lower than 1 with kosmotrope anions. The origin of this distinction has been ascribed to the ability of anions to cause pitting through the thin passive film at the aluminum surface, which depends on the varying resistance of the anions to dehydration. The influence of the nature of the cation of the supporting electrolyte on the efficiency of electrocoagulation has been investigated by comparing the same treatment of two characteristic colloidal samples. While removal efficiency is better for a positively charged latex in the presence of sodium chloride, it is better for a negatively charged oil in water emulsion in the presence of ammonium chloride. The results come from different effects of pH and its influence on aluminum species during electrocoagulation.