Methods of treating aqueous coolants in open circulating water cooling tower systems are provided. The methods including placing a controlled release additive composition in contact with an open circulating aqueous coolant in an open circulating water cooling tower system. The controlled release additive composition includes a core having at least one additive selected from corrosion inhibitors and scale inhibitors; and a coating, for example, a polymeric coating, substantially surrounding the core. The coating is substantially insoluble in the aqueous coolant, and is effective to slow the release of the at least one additive into the aqueous coolant.