Chlorine, the Swimmer’s Element

Eau de Chlorine is a badge of honor for swimmers.  It’s a sign of dedication to the sport that makes them happy.  And for teenagers it’s a better smell than puberty or any other sport provides. But such a recognizable bouquet comes with a cost: dry / brittle hair, dry skin and itchy eyes.  As a swim parent, I was interested in the chemistry behind pool maintenance which is where my fairy ninja spends most of her time and works her magic.

Disinfection for pools is necessary when you have humid conditions and humans in the water.   Chlorine is extremely effective at killing bacteria and other organisms by invading the cells and destroying the proteins that keep the cell functioning.[i] The “chlorine” smell that many swimmers and swim parents are familiar with is actually chloramine which forms when chlorine reacts with bacteria and nitrogen containing biological materials.

The most common pool sanitizer chemical is chlorine, but there are others you can use, including[ii]:

  • Bromine: chlorine’s halogen cousin and more commonly used in hot tubs and indoor pools. Bromine works a little differently than chlorine and it’s not as effective when dealing with certain types of algae. It’s not recommended for pools in direct sunlight. Sunlight eats up bromine very fast because it’s not stabilized.
  • Biguanide: It’s an effective sanitizer for swimming pools and even makes the water feel smoother. However, biguanide is provided in a specialized chemical package and is not compatible with traditional pool balancing chemicals.
  • Minerals are introduced to the water by a system that resembles a chlorinator, but they sanitize much slower than chlorine. A mineral system is not a complete chlorine alternative but it does significantly reduce the amount of chlorine needed.

When a chlorine particle attacks and kills bacteria, it floats around in the water as chloramine or other by-products.  To remove the by-products, you must “shock” the water by adding enough chlorine or other oxider to reach breakpoint oxidation. Pool shock is done overnight because free chlorine becomes inactive in sunlight and takes 8-10 hours to complete oxidation.  Oxidation of chlorine by-products by ingredients like Vitamin C is the purpose of specialty shampoos, body washes or sprays for swimmers but the ingredients need to be at a high enough concentration.

There is more to the pool chemistry than killing bacteria and viruses.  The two elements of a clean pool are sanitation and water balance.[iii]  There are three components to keeping pool water balanced: pH, alkalinity and calcium hardness.  Water balance also depends on keeping dirt and debris out of the pool.

There are milder alternatives that provide sanitization which eliminate or significantly reduce the amount of chlorine needed.

Salt-water treatment for pools sound likes a non-chlorine option but it is only another means of producing chlorine using chlorinated salts and an electrical unit that breaks it down.  It has maintenance and water balancing issues similar to traditional chlorine treatments.

Ozone systems create low levels of reactive ozone gas in water circulation systems and kill bacteria and oxidize chlorine by-products and organic materials.[iv] Caution needs to be taken that ozone stays in the water long enough to do its work but is removed or degraded to oxygen gas (O2) before reaching contact with humans or open air.  Its reactivity can be more damaging to skin and eyes than chlorine or chloramines.[v]  Well balanced and filtered ozone pools can provide water that doesn’t have the characteristic chloramine smell.

UV systems irradiate water with UV light strong enough to disinfect pool water. The process attacks the microorganism’s DNA — protozoans, viruses and bacteria are unable to reproduce and remain inactive.  Chlorine, at a significantly lower level, is used as a backup system.[vi] Irradiated water needs to be filtered same as other treatment methods.

An alternative system (brand name ClearComfort) uses a principal similar to Ozone and UV systems but create reactive hydroxyl compounds and hydrogen peroxide which are effective enough to nearly eliminate need for chlorine.[vii]

Sphagnum moss is a more recent technology for pools that is as old as nature for cleaning water.  It is not a standalone technology but works better than traditional water conditioning chemicals and is very effective on eliminating by-products of sanitization.[viii]  Pool water is contacted with the moss in line with filtration.  Moss is effective at preventing biofilm and scaling.[ix]

In summary, keeping a pool clean and balanced to avoid illness or irritation is not a simple task.  There are options to minimize chlorine quantities but all treatements need to be maintained carefully.  For more information on what it takes to keep pools balanced, check out the National Swimming Pools Foundation Certified Pool Operator program.

[i] Science of Summer: How Chlorine Kills Pool Germs

[ii] Swim University: Basic Pool Chemistry 101

[iii] Swim University: Basic Pool Chemistry 101

[iv] What is Ozone? ClearWater Tech, LLC

[v] A biased view on the negative effects of ozone but accurate science http://info.clearcomfort.com/ozone-pool-faq

[vi] Here is an article that describes the working of ozone and UV systems and one with UV system technical information

[vii] I wasn’t able to find a neutral source on the ClearComfort system but here is their website

[viii] Information on Moss treatment systems

[ix] Benefits of moss on maintenance issues

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