Performance based monitoring and additive control is a novel approach to the cost-effective protection of cooling system efficiency and economic life. Traditional open recirculating cooling water control utilizes feedback control of pH and conductivity together with a feed forward signal from a makeup water meter to control system chemistry. This paper covers the superimposition of cascade control based on performance parameters, corrosion and fouling, as a means to refine control and optimize results. The results are further enhanced via the inclusion of Artificial Intelligence logic to make direct real-time control and to integrate all of the logic into a single control system. Performance based control is thus a significant improvement over existing industry norms.