Abstract: An automatic demand chlorination system for use with a recirculation unit for a body of fluid, the body of fluid has a chemical therein. The automatic demand chlorination system comprises a chemical sensing unit for detecting the amount of the chemical and producing a signal, a chemical feed unit for feeding the chemical into the recirculation unit, an electronics unit for controlling the feeding of the chemical, and a solenoid unit for actuating the chemical feed unit. The electronics unit comprises input signal regulation means for receiving the signal of the sensing unit and generating a regulated signal; comparator means for comparing the regulated signal with a predetermined signal representative of the desired amount of the chemical in the recirculation unit and generating a chemical infeed signal; and solenoid timer means for receiving the chemical infeed signal and activating the solenoid unit.