Discussing Chlorine Chemistry


Brief History of Chlorine

Chlorine was discovered in 1774 by a chemist from Sweeden named Carl Scheele. He mixed the element Chlorine with a powdered pryslusite into muriatic acid. Chlorine was then named ‘chlorine’ because of its greenish color- stemming from the Greek word for green, “Khloros”. Today chlorine is one of the most highly produced chemicals in the United States. It’s in many products in the market. If we were forced to find alternatives for the usages of chlorine, it is believed that would drastically change our lives.

How is Chlorine Made?

Today chlorine is produced by the electrolysis of salt water. Here is a more scientific description for those of you who wish to better understand:

“Chlorine is formed when electricity is passed through 2NaCl (salt) and 2H2o (water), the atoms dissociate into C12 (chlorine) + 2NaOH (sodium hydroxide) + H2 (hydrogen). In the manufacture of chlroine, C12 is isolated in its gaseous form, and used to create other chlorine compounds used for sanitizing, bleaching, and production of plastics and related products,” (www.poolcenter.com)

Chlorine as a Sanitizer

When chlorine is added to water, a chemical reaction occurs. This reaction leaves us with hypochlorous acid and hydrochloric acid ( HOCl & HCl). Hypochlorous acid is the active chlorine. It is what does the hard sanitizing work in your pool. Different amounts of each chemical are created, and it depends on your water temperature and your water pH levels. The chlorine molecules kill microorganisms my ‘slashing’ through the cell. It destroys the inner enzymes. When this occurs, the cell is basically deactivated. The hypochlorous molecule continues slashing through all these cells until it combines with a nitrogen or ammonia compound. Sometimes it becomes a chloramine, and sometimes it is broken down (deactivating itself).

How Dangerous is Chlorine?

Like all chemical compounds, chlorine has the ability to be potentially very hazardous. Some forms of it are more dangerous than others. However, the chlorine found in water in swimming pools poses no danger for swimmers at all.  Some people may find they have an allergic reaction to chlorine, however these are rare. If you have a poorly balanced pool, chloramines may form. This can cause red eyes in swimmers but it is not dangerous. If you have a pool with extremely high levels of chlorine, it is possible the water could release enough gas from the surface to cause breathing difficulties- especially in an indoor pool. This is also unlikely. The main hazard chlorine poses is to the one who handles it regularly and administers it to the pool. If that is you, use caution and always read the directions on the label. When you open a container of chlorine, use caution. Breathing in straight chlorine can make you unconscious. It could even be fatal. We recommend ALWAYS wearing gloves and eye protection of some sort when handling chlorine. If it touches your skin accidentally, you should wash it off to prevent irritations. If you get chlorine splashed in your eye, wash you eye with water and contact a doctor right away. The most important thing to remember when handling chlorine is to NEVER MIX IT WITH ANY OTHER CHEMICAL. Mixing chlorine with any other chemical could produce something bomb-like. It could release a form of mustard gas. This can cause serious health problems, and any explosions can be extremely dangerous. To protect yourself and your family, store chlorine away from other chemicals and keep out of the reach of children.

Is chlorine dangerous for the environment? For the most part, no, not at all. Chlorine is mostly used in swimming pools and pools stay completely separate from the nature surrounding them. It is very unlikely the amount of water spilled from your pool during back washing or splashing could pose much harm to the environment. Environmental impacts have been seen on drain and clean jobs. These were situations when acid water was pumped into nearby streams.

Surprisingly, pool water is very similar to the make up of city water right out of your faucet. Many people actually water their lawns and gardens with a higher chlorine level and lower pH level than is found in their swimming pool. When deciding whether or not to use chlorine, it is important to be informed and to weigh the pros and cons.

Forms of Chlorine

Gas: In its natural state, chlorine is a gas. Chlorine gas is available for swimming pool sanitation. It is inexpensive and contains the purest form of chlorine. It is extremely dangerous and restricted in its uses. Rarely do we find a pool using gas as its sanitizer, and we do not necessarily recommend it. Gas is extremely acidic and has a pH level close to that of muriatic acid. Pools who use the gas form of chlorine also use a lot of base to counteract this.

Liquid: Liquid chlorine is created by bubbling the chlorine gas through a solution of caustic soda. It is sometimes called Sodium Hypochlorite (NaOCl). The liquid can be poured directly into the pool but we recommend using a diaphragm pump or something of the like to inject it into the plumbing. Liquid chlorine is more popular in larger, commercial pools. For residential pools, the costs do not seem to be worth it. While liquid chlorine can be cheaper than other forms, the cost of acid required to counteract it pH of 13 seems to outweigh the benefit.

Solid (tablets): Tri-chlor are tablets of chlorine. They are a stabilized form of chlorine that has achieved a great amount of use recently. These tablets are known to be ‘stabilized’ meaning they have cyanuric acid pressed into them. This acid is like a sunscreen for the chlorine molecule. It extends its life in the sun. This form is slow dissolving so it seems to work well in floating chlorine dispensers or in-line erosion feeders. Using chlorine tablets in the skimmer is not recommended because of its corrosive nature- it could ruin metal pipes and equipment. Tablets are an effective yet expensive route to controlling the growth of algae in your pool.

Granular: Granular chlorine or Di-chlor, is chlorine manufactured in the form of granules. It dissolves rapidly and goes right to work on killing pool contaminants. It can be used as a shock treatment for normal sanitation purposes. Di-chlor’s main setback is its cost. This is most likely the most expensive form of chlorine.  There are other forms of granular chlorine; however, their different properties can be complex to explain. For more information on various types of chlorine or to find the best one for your pool, call us at Ask the Pool Guy!

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