Abstract: In a chemical solution circulator including a tank, a pump with an intake pipe connected to the tank and a discharge pipe for delivering solution to an enclosure communicating with the tank; a chemical concentration control system for the automatic addition of liquid chemicals for maintaining a predetermined concentration thereof within the tank comprises a diverter and chemical additive pipe connected to the discharge pipe for continuously sampling the solution and outletting into the tank. An aspirator is connected into the diverter pipe and has a low pressure additive intake pipe connected to a chemical solution storage tank. A normally closed solenoid valve is interposed in the additive intake pipe. An electronic controller is connected to the valve. A flow through conductivity cell is interposed within the diverter pipe upstream of the aspirator for signaling the controller at a set value maintaining the valve closed.