Abstract: A process for preparing a disinfectant for use in swimming pools and the like. The process provides a formulation containing copper sulfate pentahydrate that will remain suspended so long as the formulation is maintained at a temperature above 40° F. The process includes the step of mixing the copper sulfate pentahydrate with water, sulfuric acid and ammonium sulfate at a temperature of 187° F.±10° F., then rapidly cooling the mixture to a temperature of 57-65° F. Colloidal silver or gold added to the formulation before the step of rapidly cooling will also remain suspended. Hydrogen peroxide may be added to enhance the performance of the disinfectant.