A system and method for controlling operating parameters of an industrial fluid system based on measurement of optical and electrochemical properties. The system comprises a handheld or portable meter that can substantially simultaneously measure one or more optical properties and one or more electrochemical properties of a sample of fluid from the fluid system. Information based upon the measurements or calculations made by the system may be used to manually or automatically alter various operating parameters to control the fluid system and aid in maintaining stable operation of the fluid system within preferred specifications.