What is Chlorine?
Chlorine, in any form, mixed with water forms hydrochloric acid (HC1, commonly called muriatic acid) and hypochlorous acid (HOC1), the killing form of chlorine.
Its purpose is to kill bacteria in the water. Bacteria carry disease and stimulate algae growth. Chlorine accomplishes this by oxidizing the bacteria and other waste in the water. Rust is oxidation in progress. Oxygen is, in essence, dissolving the material with which it comes in contact. Sanitizers, oxidizing in your pool are essentially “rusting away” the bacteria and other waste material in the water.
Chlorine inactivates or kill the vast majority (above 99.9%) of microorganisms that can cause disease (pathogens). Pathogens include bacteria, fungi, viruses, and protozoan parasites. In addition, disinfectants are effective at killing algae. The reason we use the word “inactivate” in addition to “kill” is that some pathogens like viruses are not “alive” and cannot be killed.
Some forms of Chlorine:
Sodium Hypochlorite (liquid)
Sodium Hypochlorite is a liquid chlorine releasing disinfectant that is the most common disinfectant used to treat pools. The convenience of feeding liquid and the relatively low cost play and important role in its popularity. The hydroxide ion (OH-) reacts with the pool or spa water to raise the pH. The strength as used at the pool is 10% to 12% available chlorine content (ACC) and has a pH of 13. The pH must be corrected by the addition of an acidic material such as muriatic acid or the injection of C02.
Calcium Hypochlorite (dry)
Calcium Hypochlorite is a dry form of chlorine often called “cal-hypo.” It is available in granular tablet, or briquette form. Depending on how it is manufactured, the ACC can vary from 65% to 78%. The amount of active ingredient and the ACC are the same with cal-Hypo. It is commonly used to superchlorinate water based on the high available chlorine content (65-78%) and its moderate solubility. One pound of cal-hypo that has either 65 or 78% ACC dissolved into 10,000 gallons of water will deliver 7.8 ppm or 9.4 ppm of chlorine, respectively.
Lithium hypochlorite is a dry, granular compound of chlorine. It is rapidly and completely soluble, making it a good choice for super chlorination. It is not widely used due to relativelily low active strength of 29% (ACC 35%) and the relatively high cost. It dissolves very quickly, making it ideal for use in vinyl-lined, fiberglass, or painted pools.
Elemental chlorine gas has both 100% active chlorine strength and 100% available chlorine content (ACC). It rapidly lowers the pH of the water and destroys its buffering capabilities. It is extremely toxic and not easy to handle, which is why it is not commonly used.
Above are the most common forms of chlorine. Liquid chlorine is the most widely used form since due to low cost and ease of use. Many people ask us how salt systems work to create chlorine and what form of chlorine it makes so we will discuss that in our next article.