How Does Chlorine Keep a Pool Clean?

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There’s nothing quite like the luxury of a swimming pool. Conveniently located at our schools, local gyms, or, if we’re lucky, our own backyards, pools offer all the joys of lake or ocean swimming and none of the hazards. The water is crystal clear, with no jellyfish drifting invisibly in our path, and no jagged debris lurking underfoot. There are no riptides to drag us out to sea, or unexpected drops into deeper depths.


Best of all, pool water is totally sanitary. There are no dangerous microbes breeding in it, and no slime of algae to cling to you when you dive in. This is not a magical property of the pools themselves, and, if you’ve ever been in a public pool, you probably have some idea what is responsible for keeping that water clean. That’s right, I’m talking about chlorine.



What is Chlorine?


Atomic number 17 on the Periodic Table of Elements, chlorine is a naturally occurring element that is rarely found on its own in nature. This is because it is highly reactive with other elements it encounters. One of the most abundant sources of chlorine is table salt, the result of a bond with sodium.


It is this reactive quality that makes chlorine ideal for pool cleaning. In a different form, chlorine is actually essential to the biological processes of life. Our bodies actually require it. Dissolve it in water, however, and you get something else entirely.




How Does Chlorine Clean Pool Water?


Chlorinating water is a process that begins with isolating chlorine from one of its compounds, usually salt. The salt is dissolved in water, forming a brine. Next, an electric current is applied to the brine to separate the elements. This process is called electrolysis.


The pure chlorine can be mixed into water in its gaseous form, or new compounds can be made to allow for different methods of delivery. Liquid bleach is one such compound, as is calcium hypochlorate, also known as bleaching powder. When any of these is mixed into water, yet another compound is formed as the chlorine breaks down: hypochlorous acid.


This acid is what actually sanitizes pool water. It is a potent sanitizing agent, known to kill E. Coli within .01 seconds of exposure, and shut down other germs within minutes. However, as it acts on contaminants, the acid concentration decreases. The balance between hypochlorus acid and chlorine yet to be converted can be measured to determine if your pool requires its next dose of chlorination.


According to the CDC guidelines on disinfection, the level of free chlorine in your pool must equal or exceed 1 ppm in order to be effective. The introduction of contaminants will lower this number, as will exposure to sunlight. Check your readings frequently to maintain a sanitary swimming environment.



What About Saltwater Pools?


Saltwater pools are often presented as an alternative to chlorine pools. The truth is that they achieve their sanitation by chlorination as well. While traditionally chlorinated pools are dosed directly with concentrated sources, saltwater pools are equipped with machinery that essentially performs electrolysis on the water while it is in the pool.


The result is a pool with mildly salty water and lower chlorine levels, but that is just as reliant on chlorine for sanitation.

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