A method and an apparatus for retrofit hydrolization of seawater for production of halogen biocides in situ. A method for effecting an in situ generation of biocide as an aid in anti-biofouling of a device disposed in a volume of salt water includes a) associating a cathode electrode to the device； b) associating an anode electrode to the device with the anode electrode spaced apart from the cathode electrode； and c) hydrolyzing one or more components in the volume of salt water to generate a halogen biocide at the anode electrode with the biocide flowing from the anode electrode away from the cathode electrode as a biocide film, the film responsive to a physical arrangement of the associations of the electrodes with the device.
