Abstract: Disclosed is a wet processing station in which control of the PH of the processor liquid is mandatory within predetermined limits, the processor including a tank having means to subject product to a bath of processing liquid. A PH monitoring probe is positioned in the tank with a pump in the tank for mixing processing liquid therein. The pump has a liquid intake and a discharge, the intake being positioned closely adjacent to the probe so that liquid being mixed in the tank will flow across the probe into the intake of the pump. A processing liquid concentrate holder is coupled to liquid concentrate carrying means which connect the holder to the probe, the liquid carrying means having an outlet which is positioned to discharge concentrated processing liquid directly onto the probe. Probe monitoring means which is responsive to the output of the PH monitoring probe provides a signal output when the PH of the processing liquid reaches at least a predetermined lower limit.