Breakpoint Chlorination

- do you get a strong Chlorine smell from your pool?

That's because there is not enough Chlorine in the pool; what you can smell are chloramines

Despite what many swimmers think, the biggest cause of these problems is insufficient free Chlorine rather than too much

Tricloro instantly forms Hypochlorous Acid when dissolved in water and, ideally, we have 1-3 ppm in a well-balanced pool.  Chlorine levels of up to 10ppm are not able to be detected by odour alone (although 10ppm is too strong a concentration for swimming) so if you smell Chlorine from the pool the chances are that it is high levels of chloramines

Chlorine reacts with organic substances such as sweat, body oil and urine and destroys them in a process very similar to combustion. It's only when the 'combustion' process is not completed, that chloramines remain the pool - and that swimmers notice a strong smell and suffer from red-eye and/or skin irritation (see an analogy below*)

As the process of breaking down the organic substances continues, by-products of Chlorine sanitation are formed. The by-products are called 'chloramines' and it is these compounds that are responsible for red eyes, itching skin and the respiratory problems that often affect swimmers

As Chlorine sanitizes the pool 3 stages of chloramines are formed: -

  • Monochloramine - the principal cause of red-eye
  • Dichloramine - the principal cause of sore throats and the distinctive 'chlorine odour'
  • Trichloramine - the cause of reduced oxidation of contaminants (algae can proliferate)

A pool that is sanitized by Chlorine has all 3 of these compounds at the same time and it is only when the concentration of any particular chloramine gets too high that a problem occurs

Chloramines form naturally, as outlined above, but if there is insufficient free Chlorine available to completely destroy organic matter the process comes to a screeching halt and chloramines remain in the pool, causing all the symptoms above

The way to rid a pool of chloramines is to add sufficient Chlorine to enable the chemical process to become complete, at which point the chloramines are broken down to harmless substance like nitrogen and salt

One excellent way to reduce the build-up of chloramines is to beat the bathers through the shower before they enter the water - wash that sweat and those body-oils off and bathers will have a more comfortable experience in your pool!

Add enough Chlorine to raise the level of free Chlorine to around 10 times the level of chloramines. This is best done by Superchlorination or the addition of Non-chlorine Shock

*When you have a garden-waste bonfire in the back yard, and the fire burns out completely to a fine grey ash, there is little or no smell associated with it.  However, if the bonfire is extinguished by rain before it has burned to ash - it smells, very strongly, of . . . . 'wet bonfire'

Have you ever walked past a burned-out building after the Fire Brigade has put the fire out? It stinks, doesn't it?

The same thing happens in your pool if there is not enough free Chlorine to completely destroy organic contaminants (chloramines) - it stinks!


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Ken Walker - MyPoolGuru©