compounds which contain copper are not recommended. Chlorine and chlorine containing compounds are effective algaecides and slimicides. If used, chlorine should be added as intermittent (or shock) treatment only as frequently as needed to control the slime and algae. Chlorine and chlorine containing compounds should be added carefully since very high levels of chlorine may occur at or near the point of entry into the circulat- ing water system.
FOAMING–Heavy foaming sometimes occurs when a new tower is put into operation. This type of foaming generally subsides after a relatively short period of operation. Persistent foaming can be caused by the concentra- tions of certain combinations of dissolved solids or by contamination of the circulating water with foam-causing compounds. This type of foaming can sometimes be minimized by increasing the blowdown, but in some cases foam depressant chemicals must be added to the system. Foam depressants are available from a number of chemical companies.
MAINTENANCE OF FILL PERFORMANCE
Owner must keep water clean by treatment, screening, or filtering 
Warningto avoid the possibility of fill clogging and loss of thermal perfor-
mance.
Potential Causes of Fill Clogging:
•Suspended materials—Trash, etc.
•Scale—Can be sulfates, silicates, carbonates, or oxides. Scaling effects can be accentuated by suspended muds.
•Algae and/or Slime—Can control with chlorine or non-oxidizing biocides.
Possible Sources of Scale:
•Calcium Sulfate—From make-up and sulfates produced by sulfuric acid for pH adjustment. Calcium sulfate should be kept below 1000 ppm expressed as CaCO3.
•Calcium Carbonate—Generally will not form scale in the cooling tower if carbonate scaling does not occur in the condenser.
•Exceptions: If make-up water contains surplus free carbon dioxide, scaling may be inhibited in the condenser, but may occur in the tower fill because of CO2 stripping.
•Silicates and Oxides—Silica scale is virtually impossible to remove. Silica
scale is unlikely if SiO2 is held below 150 ppm. Oxides, such as iron oxide, can coat all parts of the system if soluble iron is present in concentrations above 0.5 ppm. Iron oxides do not usually develop into thick scales but can accentuate the development of other scales.
