A method and composition for reducing chemical oxygen demand is presented. The composition includes a persulfate donor, a transition metal catalyst in contact with the persulfate donor, and a cationic electrolyte. When the composition is contacted by water, the transition metal catalyst reacts with persulfate and reduces the persulfate concentration in the water. The composition allows the use of persulfate, which is known to cause irritation to users of aquatic facilities (e.g., pools, spas) that come in contact with it. As the persulfate concentration is reduced rapidly in the water by the catalyzed reaction, the persulfate-containing product may be applied while the aquatic facilities are being used. A free halogen donor may be incorporated into the composition. The composition may be in the form of powder, granules (coated or uncoated), or agglomerate. The cationic electrolyte facilitates the removal of the catalyst from the water.