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Cool clean water: a guide to nonchlorine pool water treatments. (In Depth).

By far the most common pool treatments use some type of chlorine. Few alternatives are as inexpensive, or as effective by themselves at both killing bacteria and breaking down organic contaminants, such as algae, soap, suntan lotion, skin cells, spit, sweat, and urine, that accumulate in pools and spas. But even though the Environmental Protection Agency has approved chlorine compounds for swimming pool use, some custom home owners question the health risks of chlorine and are demanding nonchlorine treatments.

John Gedney III of E.L. Wagner Custom Pools, an award-winning pool builder in Bridgeport, Conn., says he simply can't afford to have a pool owner potentially mishandle chlorine, which could lead to a buildup of chloramines, a by-product of chlorinated pool treatments that can cause slimy skin, dry skin, skin rashes, and a potent chemical smell (see "Chlorine Chemistry 101," page 00). Instead, he relies on ozone, used in conjunction with a mild bromine sanitizer.

Ozone is just one example of an increasing number of nonchlorine pool treatments that are finding expanded markets in the United States. Many of these products have been developed in Europe, where they have a significant track record. All of them are more expensive than the average chlorine treatment, and (like chlorinated treatments) all require a periodic shock--an extra-high dose of a chemical treatment (applied when no swimmers are in the water) to control aggressive algae, slime, and water molds. Here's a rundown of the nonchlorine products.


Bromine is more unstable than chlorine in sunlight (as much as 75 percent of the free bromine in a pool can be depleted by the sun in just two hours), so it is not by itself a viable alternative to chlorine. However, in conjunction with an effective oxidizer (a treatment that will break down the accumulation of dead organic matter), it can be used in very light doses to disinfect. Bromine is much more effective than chlorine in hot water, so it is a common treatment for spas and hot tubs. Formulations typically have a low pH of 4.0 to 4.5, creating an acidic solution. Depending on the amount of bromine used, the pH of the water may have to be adjusted with soda ash, a relatively benign additive compared with those used to balance the pH in a chlorinated system.

Biguanide With Hydrogen Peroxide

Biguanide is a polymeric compound that essentially asphyxiates microorganisms rather than tearing apart their cell structures. Originally used as a germ killer in pHisoHex soap, contact lens solutions, and liquid makeup, biguanide is sold as a pool and spa treatment under the brand names Baquacil, Revacil, and SoftSwim. All of these products are sold as complete systems that include a hydrogen peroxide shock treatment, as well as a line of other compatible water treatments that can treat incidental outbreaks of aggressive algae and bioslime.

Biguanide is much more stable than chlorine or bromine. It is not affected by sunlight and heat or minor fluctuations in pH, so treatment only needs to be added to the pool water twice a month, even with heavy pool use. Because biguanide does not attack the cell structures of organisms, it is considered much milder on skin and swimwear, pool equipment, vinyl liners, and landscaping.

Minor drawbacks to biguanide are that any leak in the filtration system may cause foam to collect on the pool surface (think of the foaming action of pHisoHex), and it does not decompose dead organic matter, putting more demand on the pool's filter. A dirty filtration system can cause the water to grow hazy or organic debris to accumulate at the waterline more easily than with other treatments. Once a year or so, the filter must be isolated, then cleansed with nitrochloric acid. A biguanide pool must be shocked with a hydrogen peroxide solution every one to two months to control algae blooms and pink slime and to decompose dead organic matter.

Ionization Systems

Ionizing water purifiers were developed by NASA to disinfect water on Apollo space missions and have been developed for commercial drinking-water treatment as well as common pool sanitation. The systems work by placing two electrodes made of copper and silver in the circulation pipes. When the electrodes are energized by low-voltage electricity, charged ions move back and forth between the probes, and water flowing past them carries the ions into the pool.

An aqua catalyst system is a derivative process that is installed in line after the pool pump. As pool water flows over copper/silver beads in the system's chamber, the beads bounce back and forth, creating an extra molecule of oxygen. In the case of both aqua catalyst systems and ionizers, the pure oxygen or the ions discharged into the water can molecularly alter the structures of contaminate molecules and kill microorganisms.

Ionizers require a weekly addition of a small amount of nonchlorine shock to burn off the dead organic matter and kill aggressive algae and slime. The initial cost of an ionization system is high, but the long-term savings in chemical disinfectants provide a substantial payback. The biggest drawback to a copper/silver ionizer is that copper ions will eventually stain pool surfaces. Clients must be made aware of this and that there are stain removers available to combat this problem.


Ozone, a gas composed of three oxygen atoms, is a very effective disinfectant that oxidizes much better than chlorine. But it is extremely unstable and must be used in conjunction with light concentrations of another sanitizer, such as bromine or chlorine, to maintain an effective level of disinfectant in the pool at all times.

For pools, the most common type of ozone generator is known as a corona discharge unit, which works by creating small electrical arcs inside an air-filled chamber. The strong electrical charges split some oxygen molecules in half, creating single oxygen atoms, which attach to remaining oxygen molecules, forming ozone ([0.sub.3]).

Because ozone is very unstable, it must be replenished continuously and may be unable to tolerate heavy swimming demands without further additives. It also should not be used to treat indoor pools without powerful ventilation equipment.

UV Systems

Ultraviolet radiation has the power to destroy microorganisms by penetrating their outer cell membrane and can be used to disinfect spas. UV units consist of a lamp and a quartz sleeve, which is placed inside a cylindrical chamber. The sleeve distributes UV light into every part of the cylinder, zapping pool water as it's pumped through it. Like ozone, ionization, and biguanide, UV systems need periodic chemical shocks. A UV system won't work if the water is cloudy, because the rays will be screened, and, at least so far, the units can't disinfect water fast enough to keep up with the demands of an entire pool. * Clayton DeKorne is a science and technology writer based in Brooklyn, N.Y.

Chlorine Chemistry 101

All pool treatment systems work at the level of the infinitesimal, altering the chemical structures of microscopic contaminants in a subatomic swap meet of electrons and ions. You don't need to be a chemist to use them, but a basic understanding of the chemistry involved may help you guide customers past some of the manufacturers' confusing chemical jargon, which can sometimes be misleading. One natural salt treatment, for example, purports to eliminate "obnoxious chemical compounds." But when the salts are passed through the system's generator, which is plumbed into the pool's circulation equipment, they get an electrolytic charge that changes the salt (sodium) to sodium hypochlorite, also known as chlorine. Then, the chlorine goes to work just as it does in any chlorinated treatment. While the concentration of chlorine atoms may be lower, that is likely to make pool sanitation worse, not better.

When dissolved in water, chlorine compounds recombine to produce hypochlorous acid, the "killing form" of chlorine. This acid attacks bacteria by oxidization--the extraction of electrons in a chemical reaction that literally burns up the cellular structures of organic contaminants. For this reason, chlorine is often touted as "both a sanitizer and an oxidizer"--that is, it both kills the organisms that bloom in warm water and dismantles their dead bodies.

While the active agent in a chlorinated pool is an acid, the other components dissolved from the treatment create a very basic (high pH) solution. At high pH, hypochlorous acid easily ionizes (meaning it gives off electrons), rendering it ineffective at breaking apart organic materials.

To lower the pH and boost the effectiveness of chlorine, treatments often require the addition of muriatic acid or sodium bisulfate, compounds that health-conscious clients may object to as well. Chlorine also dissipates easily in sunlight. Stabilized formulations (chlorinated isocyanurates) are generally more stable than the more common calcium hypochlorite (in sticks, tablets, or granules) and sodium hypochiorite (liquid bleach).The isocyanurate--the "conditioning" portion of stabilized chlorine--effectively blankets each chlorine molecule, protecting it from ultraviolet light and allowing it to dissolve more slowly, so the chlorine is available over a longer period of time. The addition of cyanuric acid can extend the life of any chlorine product, though it, too, is a toxic substance that must be diluted to minimal concentrations.

Too much chlorine can be irritating to swimmers, but too little is dangerous. Too few chlorine atoms available in a pool to meet the killing demand won't oxidize, or burn up, contaminants. Instead, they will tend to bond with simple nitrogen compounds, such as ammonia and urea, creating chloramines. Chloramines eventually accumulate in any chlorinated pool, but they accumulate much faster in an undertreated pool. These are the compounds responsible for the strong chlorine smell, stinging eyes, chafing, and slick skin associated with poorly maintained chlorinated pools.

To control chloramines, a pool must be periodically "shocked" with an extra-strong dose of chlorine. Shock treatments also contain extra algicides, as well as other additives to control slime molds, and treatments to soften hard water, which may be required to prevent mineral buildup (scaling) on pool surfaces.--C.D.
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Author:DeKorne, Clayton
Publication:Pool & Spa News
Date:Apr 11, 2003
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