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

* Sodium hypochlorite becomes an inert substance rapidly in heat and sunlight so it should be stored in a clean, well-ventilated, dark, dry place. It should never be placed near paint, fuel, solvents or paper, or other types of chemicals. Owners should not buy more than they can use in a two-week period.

* Due to sodium hypochlorite's high pH, pool owners may need a lot of pH adjustment chemicals to bring it into range.

* Calcium hypochlorite doesn't dissolve fully, so if someone merely broadcasts it over the water rather than using an erosion feeder, the calcium can damage pool surfaces. Black-bottom pools may develop white spots; white plaster may stain.

* Dichlor's stabilization also counts as a negative. It lacks the activity of an unstable compound, which allows cyanuric acid to build up, requiring technicians to drain and refill the pool more often. The cyanuric acid also ties up the chlorine and reduces the oxidation-reduction potential (ORP), requiring higher amounts of chlorine over time to accomplish the same tasks.

* Isocyanurates, or stabilized chlorine compounds, aren't needed for indoor pools. Technicians use these chlorine compounds to prevent chlorine loss due to ultraviolet light exposure, which typically isn't present indoors.

* Trichlor's acidic 2.9 pH makes floating erosion feeders problematic. Prevailing winds blow these dispensers to the same spot, where the chemical destroys the surface in that area.

IONIZER/MINERALIZER

How it works: Ionizers rely on two dissimilar metals--often copper (an algaecide) and silver (a bactericide sanitizer)--to create electricity and impart these metals to the water. In some cases, water movement provides the transport.

This treatment works great on scale buildup, according to Cal Robinson, owner of CDE Research in San Diego. That's because the ionization process turns calcium carbonate (the hard scaling form of calcium) into calcium bicarbonate, which stays soft and remains dissolved in the water. Also, the dissolved calcium in the water attracts calcium in the carbonate form, slowly reducing existing scale buildup. Finally, the copper ions are attracted to the calcium in the water, forming a semisolid to be caught in the filter.

Facts to Remember:

* Ionizers lack an oxidizer, so NSF International (formerly National Sanitation Foundation) standards still require at least a 0.4 part per million chlorine or 0.8 part per million bromine level in the water to be effective. In theory, ionization and chlorine provide synergetic benefits, but studies show the cost benefit is negligible.

* It's difficult to control the amount of metals entering the water, so they may stain the walls and turn green the blond, white or gray hair of swimmers. Chlorine often gets blamed for this phenomenon, but copper is at fault.

* TDS buildup interferes with the current flow between electrodes, making it hard for them to do the job of slowing the rate of metals entering the water.

* Pool owners must replace the cartridge or replenish the mineral bed on the schedule set by the manufacturer.