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

* Bromine and some ionizer/mineralizers won't work together in a pool because at that temperature, bromine precipitates with the silver, which knocks out two of the three needed cleaners. Spa temperatures change silver's solubility, so some devices will work under those conditions.

OZONE

How it works: This system uses either ultraviolet light or, most commonly, corona discharge to generate ozone (activated oxygen/[O.sub.3]) as the oxidizer, sanitizer and flocculent.

An effective slipstream system first captures ambient air, dries it and enriches the typical 21 percent oxygen content before passing it into an ozone generator. Here, a series of high-energy electrodes split these [O.sub.2] molecules into very unstable individual O atoms that recombine as equally unstable [O.sub.3]. Venturi jets inject the ozone into a slipstream of water drawn off the main line, where the water and ozone must remain in a contact chamber two to four minutes. A granulated activated carbon (GAC) filter, or manganese dioxide catalytic converter, strips out the ozone before the water rejoins the pool.

Ozone is very unstable; its activity makes it much faster at sanitizing and oxidizing than chlorine would be against the same pathogen. Owners end up with better-smelling, better-tasting, better-quality water because of reduced chemical usage.

Facts to Remember:

* As many as 90 percent of the ozone systems Osinski sees are not sized or installed properly. It's not a one-size-fits-all proposition with these systems. Inexpensive systems lack the oxygen generator necessary to boost the ambient air, so the system fails to produce enough ozone to make an impact. Installers also plunk it on the return line, where the water only remains in contact for seconds before returning to the pool, where it creates bubbles and off-gases into the environment and reacts with chemicals injected into the return line, according to Osinski. Although it's important to keep these facts in mind, a properly installed ozone system can be trouble-free.

* Ozone destroys chlorine; chlorine destroys ozone. So they must not come into contact with each other at any point in the system. If they do, the homeowner actually winds up using more halogen product than without the ozone system.

* In a brominated pool or spa, the ozone generator activates the bromine salt (sodium bromide) in the water and forms HOBr acid, the activating sanitizer. Any oxidizer (chlorine, nonchlorine oxidizers, potassium peroxymonosulfate or an electrical charge) would create the same effect.

* A typical slipstream system draws off approximately 25 percent or more of the circulated water for ozone treatment, which adds to a 24-hour cycle to turn over the entire pool through this process. Homeowners who do not circulate 24 hours a day slow down this sanitization too much. If the water is not circulating for 24 hours, it will take several days for the water to go through a single cycle.

POLYHEXAMETHYLENEBIQUANIDE (PHMB)

How it works: This product is not sold by generic name. It imitates the anti-microbial scrubs used in hospitals: It disinfects by penetrating the bacteria cell walls, causing them to burst from within. It also serves as a flocculent, wrapping particles in a heavy gel, which sinks to the bottom for vacuuming. It, too, needs an oxidizer companion; a hydrogen peroxide-based, brand name oxidizer is the most compatible and readily available, says Osinski.