The science of sanitization: a detailed, understandable guide to the sometimes inexact science of pool and spa sanitizing - Close up: sanitizing

Pool & Spa News, August 22, 2003 by Julie Sturgeon

Pool and spa sanitization is not an exact science.

Sure, the concepts behind sanitization boil down to the immutable laws of physics and chemistry. But variables such as bather loads, location, source water and even the presence of landscaping materials all play a role in how a pool or spa should be maintained and which chemicals work best.

There is no one-size-fits-all answer.

So the best thing service technicians, retailers and consumers can do is try to understand how the different types of sanitizers work and pick the one that fits their pool, spa and lifestyle best.

To that end, here's a breakdown of the major kinds of sanitizers:

BROMINE

How it works: Bromine also is a halogen. Two forms of bromine are commonly used for pool and spa water treatment: sodium bromide and BCDMH.

It is most commonly used as a compound that splits into hypobromous acid to sanitize, and bromamines that bond with the organic impurities in the water. At normal pH levels of 7.5 percent, roughly 47 percent of chlorine forms hypochlorous acid, whereas 94 percent of a bromine compound forms hypobromous acid under the same conditions, making it a more concentrated sanitizer. That's why most swimming pools rely on 1-bromo-3-chloro-5, 5-dimethyl-hydantoin (BCDMH) tablets that are typically 66 percent bromine and 27 percent chlorine to serve as the oxidizer.

Bromine also remains stable at high temperatures where chlorine dissipates still more rapidly, which is why many technicians recommend bromine for spas.

Facts to Remember:

* Use bromine only for residential spas because bromine's strength lies in sanitizing, not oxidation, says Alison Osinski, owner of Aquatic Consultants, San Diego. Most spas battle organic loading oxidation.

* The Centers for Disease Control reports that approximately 5 percent of the U.S. population develops a sensitivity to chlorine. Researchers have determined that number jumps to 17 percent with reactions to bromine.

CHLORINE

How it works: To date, chlorine is one of the most effective disinfectants, says Dave Miser, owner of Underwater Unlimited in Greenwood, Ind. More than 98 percent of the United States' drinking water supply is treated with chlorine, and more than 10 million tons of chlorine are used annually in North America.

Adding Cl2 to [H.sub.2]O creates a sanitizing hypochlorous acid (HOCl) and HCl, aka hydrochloric acid or muriatic acid. After this reaction, HOCl's hydrogen ion disassociates, leaving a negative hypochlorine ion (OCl-) seeking a positive charge such as nitrogen and ammoniated impurities in the water. When OCl- combines with these impurities--such as sweat, urine, hair-care products, deodorants, pollution, landscaping materials, leaves--it creates combined chlorine, or chloramines. Chloramines bear responsibility for the recognizable odor, itchiness and eye irritation that bathers note.

Most pool owners choose one of four compounds:

1. Sodium hypochlorite: chlorine gas mated with sodium hydroxide. You could substitute Clorox brand bleach from the grocery store in a pinch, says Osinski, but the bleach concentration would be between 5 and 6 percent available chlorine vs. the 12 to 15 percent from sodium hypochlorite sold for sanitizing and oxidizing pool water. It's safe to handle and nonflammable, which makes it a less hazardous product to store.

2. Calcium hypochlorite: chlorine gas passed over sodium hydroxide, or lye. Its available chlorine ranges between 65 and 75 percent, with a lower pH than sodium hypochlorite. Several methods can be used to introduce it into pool water: It can be added using an erosion feeder or erosion soaker, or it can be made into a liquid and pumped in with a peristaltic piston or diaphragm pump. Another method is for the pool owner or technician to broadcast the chemical over the water surface.

3. Lithium hypochlorite: chlorine gas bubbled through lithium, sodium and potassium sulfates, then dried. Because it's alkaline, like all hypochlorites, users need to adjust the pH downward. It is totally soluble, nonflammable and noncombustible, with a long shelf life. It's also one of the more expensive forms of chlorine.

4. Isocyanurates: chlorine products sold pre-mixed with the stabilizer cyanuric acid: Trichloro-s-triazinetrione (trichlor) and sodium dichloro-s-triazinetrione (dichlor). Dichlor began as trichlor, with sodium bicarbonate and cyanuric acid added. It's sold in 56- and 62 percent available chlorine dosages, with a neutral pH of 6.9. Trichlor is 90 percent chlorine, produced by cyanuric acid and the presence of gas chlorine, with a pH of 2.9. Both are stabilized and instantly soluble, so they create no residue or cloudiness.

Facts to Remember:

* Chlorine should not be sprinkled directly on the water surface, as is often done by homeowners, because it is too concentrated. The high concentration can harm bathers and equipment, Osinski warns. The best case would be to introduce it by using a feeder attached to the return line after the filter. Or pre-mix the chemical with water and put it in as far back in the system as possible.