Lessons on Chlorine

HISTORY

In 1774, chlorine was discovered by a Swedish chemist named Carl Wilhelm Scheele. He produced it by reacting manganese dioxide with hydrochloric acid. Mistakenly, he thought it was a compound containing oxygen. In 1810, Sir Humphry Davy confirmed it as an element and named it “chlorine” from the Greek chloros (greenish-yellow). Chlorine is a halogen and the 17th element in the periodic table, with 17 protons in its nucleus. But what we really care about is that chlorine is the most common disinfectant used to treat swimming pools, which were first used in 1897.

CHEMISTRY

Any form of chlorine when combined with water will form hypochlorous acid (HOCL), the hypochlorite ion (OCL-), the hydrogen ion (H+) and a byproduct specific to the type of chlorine being used. The HOCL is what is essentially performing the sanitizing and oxidizing, or killing off any bacteria and eliminating environmental debris and bather waste. While the OCL has the same capabilities, it is 60-100 times less effective than HOCL. Because of this, the OCL ion can bind any ammoniated compounds in the water and become less effective. This is called combined chlorine. Combined chlorine presents a problem for pools as it is not an effective disinfectant, can cause bather irritation, and environmental issues at indoor facilities.

ARTS AND LEISURE

There are a lot of myths out there about chlorine. Let’s debunk a few:

When you smell a lot of chlorine, you know the pool is clean. A strong chlorine smell means that your pool has combined chlorine (aka chloramines). As explained above, chloramines form when chlorine binds with contaminants like sweat and urine. This is an indication that actually more chlorine is needed.

Chlorine turns blond hair green. When you use bleach (a form of chlorine), what color would the stain turn your clothes? It’s white, not green. Green tints on light colored hair are the result of copper being in the water, which can bind to a bather’s hair.

Chlorine burns my eyes. Eye irritation isn’t due to chlorine. It’s due to water chemistry issues. Chlorine is very pH-dependent. In pools, we want to keep our pH between 7.2-7.8. The human eye has a neutral pH around 7.0 to 7.6, so when it is not in range, it can irritate bather’s eyes. It can also be an indication of combined chlorine as mentioned above.

Saltwater pools don’t contain chlorine. With a saltwater pool, we are not taking saltwater from the ocean and using it in our pool. Instead, we use salt onsite to generate our own chlorine through electrolysis. This produces a gentler form of chlorination, which many find soft and silky. Your pool still has chlorine and you may need to shock your pool with another form of chlorine at times.

RECESS

Chlorine has been revolutionary for the swimming pool industry. Taking the time to understand how it is made and how it works helps us better understand what is happening in our pools, leading to true enjoyment on those hot summer days when we can relax in the water—all thanks to chlorine.