Chlorine Chemistry

Ideal range: 2 – 4 ppm

chlorine chemistrySANITATION is the reduction of the level of microorganisms (living cells so small they can only be observed through a microscope) by significant numbers (usually 99.9% or more) to safe levels as established by state or federal authorities.

SANITIZER is the chemical or device that kills or inactivates the microorganisms present in pool/spa water. Chlorine, followed by bromine, are the most popular choices. Other sanitizers include ozone, biguanide (PHMB),                                                                       copper/silver ionization, and UV radiation.

Defined as a sanitizer, chlorine destroys microorganisms; however, it carries out an additional function as an oxidizer. This oxidation is the “burning up” of organic contaminants introduced to the water by the bather (e.g., hair gels, deodorant, suntan lotion, body oils, perspiration, etc.) and the environment (e.g., pollen and dirt). Studies have shown that only 10% of chlorine is needed for sanitation while 90% of chlorine is used for oxidation.

Microorganisms and organics consume chlorine. This consumption is called the chlorine demand and is defined as the amount of chlorine that will react with contaminants before any chlorine is left unreacted.



Microorganisms are living creatures too small to be seen by the naked eye and are constantly introduced into the pool by rain, wind, and the human bather. Algae, bacteria, fungi, protozoans, yeasts, and viruses are the kinds of organisms of concern. Most organisms are harmless to the human body but others are disease- and infection-causing. If not killed, these “germs” are transmitted via water to other bathers.

Non-living organic contaminants are also objectionable. An active adult swimmer can lose a pint of perspiration or more per hour. Perspiration is loaded with compounds resembling the chemistry of urine. The body is also constantly shedding microscopic skin particles sloughed off by the friction of water. These are all “involuntary wastes.” Add in “voluntary wastes” such as expectorate, nasal discharge, fecal matter, and urine and you begin to appreciate the bather load created.

Organics cause pool water to become dull, listless, and cloudy. Periodic addition of an oxidizing chemical (called shocking, or superchlorinating specifically when chlorine is used as the oxidizer) will rid water of these contaminants, leaving it sparkling and inviting.

 -chlorine chemistry