Calcium Hypochlorite

July 30, 2001
From Drinking Water To Swimming Pools

About the author:

Joanne Funyak is the Accu-Tab

marketing manager for PPG Industries, Inc., Pittsburgh. She can be reached at [email protected].


It was more than 90 years ago that Booton, N.J., became the first utility in the nation to use chlorine to purify water. Subsequently the use of chlorinated water became the norm across the country and safe drinking water is something we all take for granted. In that respect, how many people realize how water chlorination affects other aspects of everyday life? To many people, a nice dip in the pool provides recreation and relaxation, and they don’t need to think about the effort that went into the treatment and sanitation that made that pool a safe and clean place for fun. That is left to the professionals and drinking water fundamentals that can be applied to pool water care.

The pool and spa industry has spent decades perfecting the process of water chlorination using different forms of chlorine and a variety of delivery systems. Chlorine gas and liquid bleach had been the standard in commercial pool chlorination. However, two major concerns have pushed the commercial pool industry to look for alternative methods: the concern for the public, for pools and waterparks to remain free from bacteria such as E. coli and other pathogens, and chemical storage and handling concerns for both the public and pool employees. These become even bigger concerns as teenagers and seasonal help often have the responsibility for administering the chlorination system.

In response to these concerns, the commercial pool industry is returning to the old reliable form of chlorine, calcium hypochlorite (cal hypo) as their system for water chlorination. It is a dry form of chlorine that is safer to handle.

Chlorine gas requires separate vented rooms and personnel need to be trained and wear breathing apparatus when servicing or changing cylinders.

When handling liquid bleach, personnel also must wear the proper protective clothing. Bleach should not be stored near any acid products. Numerous incidents have been reported where acid and bleach were mixed, producing chlorine gas resulting in temporary evacuation of aquatic facilities.

There are many chemical advantages to cal hypo. Cal hypo contains approximately 65 percent chlorine as compared to the 12 percent that is typical in liquid bleach. Bleach breaks down over time, losing its strength and efficacy as well as adding to the total dissolved solids in the pool. Cal hypo has a neutral pH that can reduce the need for auxiliary treatment chemicals. When mixed with water, cal hypo has a pH of 10.8, making it easier to maintain the optimum pool water pH of 7.2—7.6 when compared to pH extremes of other forms of chlorine.

The calcium contained in the cal hypo is less corrosive than other forms of chlorine to pool components such as concrete, plaster and piping. Bleach can corrode pipes and electronics in the filter room. Feed pumps can lose their prime due to oxygen forming as the bleach decomposes, interrupting reliable feed of chlorine to the pool. Chlorine gas can corrode supply line fittings, which then can clog the tiny openings in the regulators and eductors used to control its addition.

By combining the popularity of cal hypo in a convenient 3-inch tablet form with a patented erosion feeder, cal hypo has made a dramatic comeback. Individual feeders are capable of delivering chlorine with the versatility of handling wading and zero-depth pools to approximately one-million-gallon wave pools and two-million-gallon standard pools. Tablet erosion systems are designed to provide even chlorine distribution. A sidestream of circulating water is directed into the chlorinator to erode the cal hypo tablet as it passes over the sieve plate and discharges through the outlet. The amount of chlorination is controlled by the water flow. Since the chlorine solution produced in the sidestream is only approximately 200 to 400 parts per million (ppm) chlorine, it will produce an overall concentration of one to three ppm, preventing severe over-chlorination.

From drinking water to food and beverage processing to commercial swimming pools, cal hypo is becoming a preferred alternative to chlorine gas and bleach. Some erosion tablet feeders not only carry the NSF 50 listing for pools but they also have NSF 61 certification for potable water and are dependable enough to be used nationwide in a wide variety of other applications ranging from wastewater treatment to food processing. Pool managers, waterpark personnel and municipalities alike are all finding that cal hypo tablet technology makes a difference. Not only do they have a consistent delivery of chlorine but they also are seeing a reduction in down time for maintenance and repairs, and fewer injuries and accidents related to other chlorine delivery methods. And all of these are providing safe, clean, clear water for their customers to enjoy.


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