Set 2 PH online monitors, one at 5m front of the pipe mixer and one at 5m back of the pipe mixer to realize the real time PH online monitoring and control. When the PH valve is out of the preset valve detect by the front PH online monitors, the acidic or the alkaline dosing system will automatic start under the control of the PLC. At the same time, the back PH online monitors will detect the PH of the water after dosing. If the dosing system is less dosing or over dosing, the PH valve will overflow the preset valve. The PLC control system will alarm or close the PH dosing system.