If you’re a hands-on pool owner, you’re used to dealing with a variety of chemicals, from chlorine to your Aunt Edna’s homemade suntan lotion. You might even already use calcium hypochlorite as your pool shock. And if you do, you’re ahead of the game. You know it’s widely used. You know it’s powerful. But what you might not know is why this powerful chemical makes the best pool shock. So if you’re not using calcium hypochlorite, understanding its origins, function, and best way to use it can help you enjoy a safer and more sanitary swim.
What is Calcium Hypochlorite?
As a pool owner, you might know this chemical compound best from the ingredients list on a container of pool shock. But calcium hypochlorite—also known as cal hypo or, in earlier centuries, as chloride of lime—has been used to sanitize water since the middle of the 19th century. Calcium hypochlorite is created by treating lime (calcium oxide) with chlorine gas. The resulting compound is a very strong base, usually sold as a granulated solid. It’s quite reactive with organic compounds and has a high pH level. It’s also readily available, reasonably priced, and easy to store and use. All of these features make it the ideal choice for shocking your pool.
Corrosionpedia Explains Calcium Hypochlorite
Calcium hypochlorite is a white or grayish white granular powdered solid with a pungent odor, which is corrosive and toxic. When calcium hypochlorite is dissolved in water, it gives off heat and nascent oxygen. When it reacts with organic substances and oils, it brings about combustion because of violent decomposition. Calcium hypochlorite is more stable than sodium hypochlorite, and contains a higher chlorine concentration (30-75%). Like sodium hypochlorite, calcium hypochlorite also increases water pH, so it is advised to acidify the water during the disinfection process.
All forms of calcium hypochlorite contain insoluble residues that form sediments in the solution. It is important to eliminate the sediment before injecting the calcium hypochlorite solution into a treated water tank to avoid clogging. Calcium hypochlorite is generally sold as 68% calcium hypochlorite combined with calcium chloride and other salts. It is used as a sanitizer in outdoor swimming pools. The calcium content hardens the water and tends to clog up filters; hence, some products containing calcium hypochlorite also contain anti-scaling agents. Localized corrosion such as pitting and crevice corrosion of stainless steels can occur in the presence of calcium hypochlorite. Calcium hypochlorite is best kept in a cool dry place away from any organic material. It is known to undergo self heating and rapid decomposition accompanied by the release of toxic chlorine gas, which is highly corrosive.
How Calcium Hypochlorite Works
The disinfecting power of this compound comes from chlorine. Commercially available varieties generally contain 65% to 75% chlorine. It also adds around 0.8 parts per million (ppm) of calcium to your pool water for every 1 ppm of free chlorine (FC), or the chlorine actively available to sanitize your pool, you add. Be sure to plan accordingly if your water already contains a high concentration of calcium. When calcium hypochlorite encounters microbes and other organic contaminants, the chlorine compounds it contains will disrupt the functions of their cells by bonding with enzymes and other cell components. This will shut down the bacteria by disabling its internal workings or destroy it by rupturing the cell walls, sanitizing your pool water.
