Abstract: A control system for automatically achieving and maintaining a desired sodium/phosphate ratio and phosphate concentration of the boiler water in an industrial boiler for minimizing corrosion. The system uses an adaptive controller that models the boiler which enables the system to predict boiler pH and phosphate concentrations at any future time given the feed rates, feed concentrations of high and low sodium/phosphate stocks, blowdown rate, mass of the boiler water, initial boiler phosphate concentration and initial pH. Once these future concentrations are determined, the controller then determines which feed rates will return the current boiler water state to, and then maintain the boiler water at, the desired sodium/phosphate congruency ratio in the least amount of time.