Clean and Balanced

Choosing the best sanitization product for your pool, i.e., sodium hydrochlorite, ozone or bromine.

By Scot Hunsaker | March 1996
Athletic Business  

A swimming pool and a leaf-strewn backyard might not seem to have much in common, but when it comes to cleaning, the processes of leaf disposal and pool sanitation are remarkably similar. Light a match to a pile of leaves and the enveloping flames oxidize them, leaving behind only smoke and ash. Likewise, to clear pool water of germs and bacteria, the industry has traditionally used chlorine gas, a halogen that oxidizes organic material in water, killing the waterborne bacteria.

Over the years, chlorine gas became the pool industry’s preferred method of sanitation. It was highly effective, relatively inexpensive and easy to monitor and deliver into the water through relatively uncomplicated systems. There were drawbacks, however. The hazardous nature of chlorine gas required special handling procedures to ensure its safe use. By the early 1980’s, as these requirements and restrictions became increasingly cumbersome, the industry began looking for alternatives to sanitizing water.

Solutions found to date have all come with trade-offs in efficiency, ease of handling or first-dollar costs (costs incurred during the installation or construction of the facility) and second-dollar costs (costs incurred during the operation of the facility). Since the choice must be made, following are some of the alternatives pool operators can choose from.

Initially, as the industry searched for a sanitizing substitute for chlorine gas, the basic philosophy was if something works, stick with it. Since the chemical was effective but potentially hazardous in its gaseous form, it made sense to try it in other forms.

Liquid chlorine (sodium hyperchlorite) is one of the chlorine-gas substitutes the pool industry has considered. It has some advantages, the most important being safer handling. In a 10 to 12 percent solution, liquid chlorine is stronger than the 5 percent solution typical in household bleach and, as a liquid, it’s also relatively easy to monitor and introduce to pool water.

Customarily, a small group injects the liquid into the main pool plumbing, through which it is disseminated into the pool. It is easy to gauge and control. First-dollar installation costs are relatively low and, at an average of $1.20 per gallon, second-dollar costs are also manageable, though still nearly three times the cost of chlorine gas.

Liquid chlorine has its disadvantages, though. First is its relatively short shelf life. Gas chlorine can be stored indefinitely in its pressurized cylinders, but stored liquid chlorine quickly loses its potency and effectiveness. At the manufacturing facility, the liquid is mixed to a 14 to 16 percent solution, but typically deteriorates to about a 12 percent solution by the time it reaches your supplier and to a 10 percent solution at poolside. Stored on a shelf for longer than a month, liquid chlorine may drop to as low as a 5 percent solution, requiring twice as much to achieve the desired effect. As a result, storing liquid chlorine can quickly become a poor investment.

Liquid chlorine also requires more physical space at the facility. In a commercial pool, it’s not uncommon to have 300 to 600 gallon storage tanks, and up to 1,200 gallon storage tanks for large wave pools. Additionally, safety codes may insist on a secondary barrier to capture the liquid in the event of a leak in the main tank.

Liquid chlorine also requires treatment to maintain the ideal 7.4 to 7.6 pH level for swimming water. To counteract the high (13.0) pH level of liquid chlorine, substantial amounts of buffering agents have to be added to bring the alkaline level down. The most commonly used agent is muriatic acid, a very aggressive substance that has significant handling drawbacks in its own right. Carbon dioxide is another frequently used buffer. It mixes with water to form mild carbonic acid, but also required more volume to achieve the desired pH levels.

To get around the handling drawbacks and short shelf life of liquid chlorine, the industry developed granular chlorine (calcium hyperchlorite). For residential pool customers, granular chlorine has been an acceptable alternative to liquid. It’s easier to handle and a barrel of it can be bought in the spring to last the whole summer. At a pH level of 12, it doesn’t require as much buffering agent as liquid chlorine. While it’s more expensive, granular chlorine has a much higher concentration of available chlorine (65 percent) than the 12 percent liquid solutions, so less is required. (It should be noted that chemicals should never be mixed, as the results of doing so with this family of chemicals can be very dangerous.)

For commercial customers, granular chlorine presented a management problem as there was no efficient delivery system to feed granular chlorine into the pool. The industry responded to that problem by developing tablet chlorine. Essentially compressed granular chlorine, tablets come in a variety of sizes. Special varieties are also available including trichlor, which is designed to be used outdoors.

With all the same benefits as granular chlorine, tablets also have the advantage of an easy and inexpensive delivery system. They are placed in feeder canisters and pool water is bypassed through the feeders, dissolving the tablets and introducing chlorinated water back into the pool. As with gas, there are fewer safety concerns and no need for the barrier systems and huge storage tanks required for liquid chlorine. First-dollar costs are lower, and even though the tablets are more expensive than liquid or gas, the need for fewer buffering agents and a longer shelf life provide trade-offs that make the operational costs manageable.

In the search to find a replacement for gas chlorine, the industry hasn’t limited itself to chlorine’s various forms. There are lots of ways to burn that pile of leaves – although some burn hotter, and others burn budgets as fast as they do germs.

Bromine is another halogen that is getting some use in the industry. Like chlorine, bromine works in the water to burn the germs, but isn’t as active as chlorine. Because of its less-active nature, there are claims that bromine is less irritating to swimmers, which is preferable at indoor sites where a buildup of offensive compounds of chlorine (chloramines) in the atmosphere can create an unappealing smell.

Bromine by itself is costly, though. First-dollar costs are acceptable, since the distribution system is similar to that used by tablet chlorine. Second-dollar operation costs, though, are significantly higher. Compared to tablet chlorine, bromine can cost just under twice as much. In addition, since it isn’t as active as chlorine, systems need twice as much to achieve the same sanitation level, making the operating costs of a straight bromine system prohibitive for many applications.

Since bromine is expensive, the industry has searched for ways to reduce the amount of the halogen used in the sanitizing process. One solution has been developed in a system that uses both bromine and ozone. When bromine is doing its job, attacking and oxidizing the germs in the water, the chemical reaction that results turns the bromine into bromide, a salt. The industry discovered that by introducing ozone – essentially oxygen with a third molecule, O3 instead O2 -into the bromide solution, the salt reverts to bromine. Through this process, according to industry suppliers, as much as 70 percent of the original bromine can be regenerated, requiring only 30 percent additional bromine tablets.

As with bromine alone, the combination of bronze and ozone creates what many supporters insist is a much more swimmer-friendly environment, both in the water and in the atmosphere. Once again, though, cost is a significant factor in determining its viability for a project. First-dollar construction costs for generating ozone can be fairly expensive. For a traditional 25-yard, six-lane pool, an ozone generating system could likely run around $25,000. Second-dollar costs for bromine can be similar to that of chlorine – even though it is twice as expensive, less is used when combined with ozone. However, the operating costs of generating ozone have to be factored in as well, including the electrical costs of running additional pumps and ozone-generation equipment.

Ozone is also an extremely effective oxidizer in its own right, so consideration has been given to eliminating the bromine altogether and running a sanitizing system based on ozone alone. This has been the focus of the industry’s most recent experiments, and the results, as with the other alternatives, are mixed.

There is no arguing ozone’s effectiveness as a sanitizer. Its use can result in pristine water. The first problem encountered by ozone, though, is that it doesn’t get along well with humans. So, before the water can be reintroduced to the pool, it has to run through a stripping filter of anthracite or activated carbon, which removes all halogens, along with the ozone.

The water that emerges from the stripping filters is very pure, but with a typical recirculating system, it will be several hours before that water again runs through the ozone chamber to be re-sanitized, and that’s a lifetime in terms of the germs constantly bombarding the water from airborne dirt, bacteria and other contaminants. An unsanitized pool full of swimmers, no matter how crystalline the water going in will quickly become unhealthy.

The answer is to add a maintenance level of halogen after the ozone has been filtered out, to keep the germs at bay until the water recycles through the ozone chamber again. Since the chlorine isn’t doing the whole job, not as much is required, resulting in better quality water and atmosphere.

The main problem with this solution is the construction cost of the ozone generating system. Ozone is created by taking air, drying and sometimes concentrating its oxygen content and running the concentrated oxygen through a chamber across a corona or sparking electrical arc, which then converts the O2 oxygen molecules to O3 ozone. (If you’ve ever smelled the fresh air after a powerful electrical storm, you’ve sensed the creation of ozone.) The resulting ozone is then introduced into the pool water where it oxidizes everything in sight, including unprotected metals in the mechanical system.

The first-dollar costs of this system are substantial. First, you have the system itself; an air separation unit for producing oxygen, the ozone-creating system and the injection system. Second is the space requirement. The ozone system is usually a substantial piece of equipment, and the addition of a required stripper tank to remove the ozone further increases the mechanical space required. Simpler, less expensive and smaller ozone creating devices that involve passing air over an ultraviolet light are available, but are used mainly for residential applications and are often incapable of providing adequate amounts of ozone for commercial facilities.

The second-dollar operational costs are also substantially greater than other systems. Because of the elaborate technical requirements of ozone, a skilled technician is required to maintain these facilities, adding to a facility’s labor costs. Those same issues have also led to some problems in reliability, and the cost of chemical treatment has to be factored in as well.

Still, despite the cost and occasional reliability problems of an ozone sanitizing system, many industry specialists think the resulting quality of the water and atmosphere is worth the trade-off, particularly in indoor environments where atmospheric quality is an issue. Furthermore, improvements in automation – not only for bromine/ozone systems, but for all the previously discussed delivery systems – continually work toward reducing the ongoing expenses of maintaining properly balanced and sanitized pool water. Precisely controlled, automated measuring and dispensing systems allow for more immediate response to demands placed upon the sanitizer, eliminating peaks and valleys in water quality and resulting in more efficient and less wasteful use of chemicals and mechanical systems.

Which system is best ? That question hasn’t been answered yet. Chlorine gas remains the cheapest, most efficient and effective sanitizer the industry has discovered. Unfortunately, it is simply no longer a choice because of the restrictions placed upon its use. With each substitute so far tested – liquid and tablet chlorine, bromine and ozone – there have been benefits and drawbacks. Mostly, though, there have been compromises, either in terms of first-or-second-dollar costs, quality of water, efficiency of use or a combination of those elements.

Meanwhile, the industry keeps lighting matches to different fires, trying to find the one that will burn up the leaves without burning holes in the users’ pockets.

MUDDY WATERS – A look at the causes of murky water.

With the sanitation system of your choice in operation, will your pool water be crystal clear? Not necessarily, if you’re having trouble with murky water, the problem might lie elsewhere.

The first line of defense is the filtration system. Water turbidity, or cloudiness, is the result of particulates, visible particles suspended in the water. The filtering system, which removes the large particles, can become compromised through mechanical failure, improper backwashing procedures or inadequate filtering media, and can fail to capture particles as it should.

Sanitation, the weapon against smaller, microscopic particulates, can be the culprit as well, if insufficient chemicals are present in the water to oxidize contaminants.

Finally, influences outside the reach of ordinary sanitation and filtration operations can also muddy the waters. Failing paint, water balance, unusually heavy use, nearby construction or severe storms are just as few factors that can create an overwhelming level of particulate matter in the water, turning an otherwise perfectly sanitized and filtered swimming pool into a milky pond.