Also Known As: Sanitizer, Bleach

Chlorine is commonly used to purify and disinfect water. Formed from salt, the element is a greenish-yellow gas that liquefies under pressure. As a disinfectant, chlorine is effective in killing waterborne diseases and bacteria, as well as algae. Chlorine also oxidizes ammonia and nitrogen compounds left behind by swimmers.

Broadly, the term refers to any kind of chlorine compound used to clean pool or spa water. Typically, these compounds are calcium hypochlorite, which is a solid, or sodium hypochlorite, which is a liquid. When these are added to water, hypochlorous acid is formed, killing pathogens. Typically, chlorine is added to the water after the filtering process.

Unfortunately, hypochlorous acid can degrade in ultraviolet light. This is why stabilizing agents, like cynauric acid, may be added. These help ensure that the chlorine works for longer periods of time.

Chlorine also interacts with other chemicals to form chloramines, which is what produces eye and skin irritations. When too many chloramines are present, superchlorination or shock treatments may be necessary. This is a process of adding a large amount of chlorine to dissolve excess organic matter and unwanted chemical compounds. As a gas, chlorine is extremely volatile and dangerous. This is one reason that the storage and handling of chlorine is paramount to good pool safety. When chlorine gas is inhaled, it can cause coughing and chest pain. Prolonged exposure can cause water retention in the lungs. As a liquid, chlorine is a skin and eye irritant, so it should be handled with care, while wearing protective skin- and eye-wear.

Containers should always be stored in a well-ventilated, dry area. All chemicals should be kept in their original containers, with the original labels and securely closed lids. Empty containers should be washed and then discarded, but not reused for any purpose, including refilling with the same chemical.