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

PHMBs do not alter pH, and their stability means they won't dissipate into the atmosphere as readily as chlorine in the presence of light. Because this chemical contains no halogens, the water contains no chloroamine odor and is less harsh on sensitive skin and eyes.

Facts to Remember:

* PHMB is the only chemical method to completely eliminate chlorine; however, this means the product is noncompatible with other sanitization

products readily available on shelves. Pool owners who choose this system are locked into the brand's shock, algaecides and clarifiers. If PHMB comes into contact with chlorine, the result is a yellowish, sludgy disaster one manufacturer describes as "scrambled eggs." Even improperly washed bathing suits retaining chlorine will stand out as a cloud of chemical reaction follows those swimming about the PHMB pool.

* Manufacturers promote PHMB systems as low-maintenance, and they are forgiving if a homeowner misses a treatment by a few days on the front end. But over time, sloppy habits accelerate the pool's balance problems.

* PHBMs' long, large and positively charged molecules build up on the filters, making it necessary to chemically clean these every four to six weeks. That includes sand filters, which many technicians assume aren't vulnerable, say manufacturers.

* One known problem with use of PHMBs is the presence of white water mold and pink slime.

* It can be more difficult to fight an algae problem in a PHMB pool than in a chlorinated one because the halogen offers more compatible weapons to try should one not respond. PHMBs are sold as part of a system, and you must use that system's algaecide.

* The product tends to impart a grayish tint to pool walls.

UV light treatment

Ultraviolet light serves as the sanitizer and hydrogen peroxide or chlorine works as the oxidizer. Often dealers confuse this UV light product with the ozone version. The difference? UV light systems treat the water, while UV ozone treats air. When chlorine is used as the oxidizer with UV light, the system is no longer nonhalogen.

The UV light system involves installing a device that contains special, low-pressure vapor lamps emitting 254 nanometer light rays on the return line. These light rays kill pathogens by destroying the nucleic acid in the cells. To be effective, UV light systems need a specific light intensity and exposure time to kill organisms: They must reach a germicidal level.

UV lamps of differing electromagnetic spectrums are available on the market. Most common is a medium-pressure, high-intensity lamp with a wider electromagnetic spectrum that is not affected by water temperature. UV systems must be installed downstream of the pool's filters; bulbs must be replaced every nine to 12 months.

UV light systems do work with chlorine, but many pool owners choose to use a hydrogen peroxide as the oxidizer because it skirts the halogen sensitivity drawbacks. And, as an oxidizer, hydrogen peroxide's oxygen-reduction potential carries a 1.3 speed rating compared with chlorine gas' slower 1.0, and bromine's 0.8, according to studies by the World Health Organization, the Water Hygiene Institute of the German Federal Health Office and the Oregon State Health Office. Robinson labels this kill rate "almost instantaneous."