Abstract: A control unit for a swimming pool electrolytic cell. The control unit includes a housing containing a logic module. An electrical connection is provided to connect the logic module to an electrical supply to receive power therefrom. An electrical connection is provided to connect the logic module to electrodes of the cell. A data outlet is provided to send control signals from the logic arrangement to a variable speed pump. The logic module is configured to: selectively supply power to the electrodes to energize the electrodes; and control the output of the pump, when the pump is active, to suit electrolytic chlorination.