Pool Water Chemistry

The Importance of Pool Water Chemistry

When pool water chemistry is properly balanced it will remain free of odor and protect bathers from bacteria and germs. Chlorine, the primary pool treatment process, kills germs and destroys harmful organic contaminants introduced into the water by bathers.

• Improperly balanced pool water chemistry can attack the indoor pool's HVAC system and the building's structural components.
• Combined chlorine compounds cause eye irritation and the so-called "chlorine odor" that swimmers often complain about.
• Free chlorine in water, under normal concentration, has no discernible odor.
• A dehumidification system will remove the excess moisture from the pool enclosure but will not eliminate the harmful chlorine compounds that cause the chlorine odor and metal corrosion.
• Only a comprehensive pool water chemistry program and continuous monitoring will keep your pool crystal clear and odor free.

Chlorine disinfects and destroys harmful organisms such as bacteria, algae, fungi and viruses, eliminating impurities that are not removed by filtration. These two processes are called sanitation and oxidation. Chlorine is introduced into the pool water by injection through the main water line supplying the pool. The chlorine immediately converts to its bacterial and virus-killing form called free chlorine. Free chlorine has no significant vapor pressure, meaning it cannot evaporate from the water in which it dissolves and carries out its disinfecting. Free chlorine consumption takes place as it reacts with organic matter, converting it to a volatile compound called combined chlorines or chloramines. A swimming pool's water treatment system automatically replenishes the free chlorine through the pool's automated chlorinator to maintain a recommended free chlorine level which is typically in the 1.0 to 4.0 PPM range.

Unbalanced Chlorine

If left unchecked, the chloramine concentration will grow to unacceptable levels with potentially harmful effects. The Pool-Spa Operator's Handbook recommends that the chloramine level not exceed 0.3 PPM. If the level is above 0.3 PPM, the corrosion process caused by the chloramines in the air is accelerated.

• A chlorine odor within the pool enclosure indicates a high chloramine level.
• Chloramines evaporating in large quantities produces a chlorine odor, and not that of the free chlorine.
• Accurate chloramine measurement requires a colorimeter, which shows the quantity of free and total chlorine in the water.
• Chloramine concentration is the difference between the total chlorine and free chlorine, as seen in the following formula:

The Dangers of High Combined Chlorines

Chloramines condense along with moisture from the pool on cold surfaces forming a corrosive chloride-rich solution. The chloride solution forms a harmful substance that will corrode metals, including stainless steel, where it forms a particularly serious stress corrosion-cracking problem. The chloramines in the air can cause significant damage to metal surfaces, such as windows, doors and frames, ductwork and HVAC equipment. The higher the concentration of chloramines in the air, the more corrosive the condensate.

The ideal method of controlling chloramines below 0.3 PPM requires periodic checking. When the chloramine level exceeds 0.3 PPM, it may become necessary to use a pool water chemistry management process called shocking. Shocking is accomplished by intentionally raising the free chlorine level in the pool to 12 times the level of the chloramines. Shocking will reduce the chloramine level to zero PPM when it is done correctly.

• Refer to the Pool-Spa Operators Handbook for tables that compare the pool size in gallons with the break point free chlorine concentration level.
• At break point chlorine level, a chemical reaction occurs converting the chloramines back to free chlorine, nitrogen gas and water.
• Free chlorine level must be raised to 12 times the chloramine level throughout the entire pool or the break point chemical reaction will not take place
• Post-shocking free chlorine level must be lowered to a level acceptable to the local health code for bathing purposes.
• Failure to completely shock the pool my be attributed to the free chlorine level not reaching 12 times the combined chlorine level in every gallon of pool water, including the water in the filter system.
• Other shocking techniques include the use of a fan to sweep off the blanket of nitrogen gas that forms over the pool's surface during shocking, and the incorporation of 100% outside air purge to remove airborne gas by-products that may interfere with the shocking process.

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