Abstract: Apparatus blending a diluent liquid, i.e., DI water, with a chemical concentrate, a flow duct and mixing tank forming a closed loop for mixing; a pair of flow duct portions each having a conductivity sensor inductively sensing chemical concentration in the blended liquid; a comparator for comparing the outputs of said parallel sensors; a single pump circulating blended liquid around the closed loop and drawing chemical concentrate from a source through an adding valve which cycles open and closed under control of the concentration sensors; the pump also propelling the blended liquid from the closed loop to the point of use, and conductivity sensors existing in individual housings through which the blended liquid flows upwardly to minimize any collection of bubbles adjacent the sensors.