Ballast and/or cooling water biocidal treatment and disinfection systems and techniques are provided. The systems utilize oxidation reduction potential control to regulate addition, or concentration of an electrocatalytically generated biocidal agent to disinfection levels in ship buoyancy and to biofouling levels in ship cooling water systems. The disinfection and biofouling control systems provide suitable treatment while reducing the potential for corrosion of ship components and, in some cases, undesirable disinfection byproducts.