In this system the pH treatment tank remains full at all time. Therefore one gallon entering the influent port displaces one gallon through the discharge port. As the influent flow enters the treatment tank it is thoroughly mixed with the tank contents. If the pH of the influent varies from the tank contents (an obvious likelihood) then the influent flow will be pH adjusted through the resultant chemical reaction that occurs as the influent mixes with the contents. There will obviously be an equal and opposite reaction within the tank contents. This opposite reaction is sensed by the pH probe which provides a continuous pH signal to the pH controller. The controller then paces the appropriate metering pump to bring the body of water within the tank back into range. If the influent flow was alkaline, for example, the result would be a steady rise in the pH of the tank contents as measured by the pH probe at the discharge port. The pH controller would then pace the acid metering pump at an appropriate rate to bring the pH back down into range.