Currently accepted practice for controlling scale, corrosion and fouling in cooling tower systems is the use of chemical addition and control of cycles of concentration. Chlorine is usually used for control of biological growths. Recent concerns over chlorine residuals and thihalomethanes (THM) in wastewater discharges, including cooling tower blowdowns, have led to evaluation of alternatives to chlorine. Ozone is one of these alternatives. Although the reasons are not immediately apparent, experience with ozone systems has indicated that ozone may also be effective in controlling chemical scaling.