Chloramines - combined chlorine problems

Pool water problem - combined chlorine (chloramines)

Chloramines are the result of insufficient free chlorine and usually result in a strong chlorine odor in and around the swimming pool. Chloramines are formed as a product of nitrogen and active chlorine (hypochlorous acid - HOCl). The nitrogen is most commonly introduced into the pool water as ammonia in the form of sweat and (unfortunately) urine.

Associated problems

Chloramines (combined chlorine) are poor sanitizers and have a gaseous tendency. The presence of chloramines (and dichloramines/ trichloramines in particular) cause the following physical symptoms:

  • red, burning eyes;
  • burning sensation in nose, throat and lungs;
  • dry, itchy skin and dry hair;
  • breathing difficulty leading to "swimmers' asthma" particularly in young children.

In addition to these, the pool has a tendency to discolor, becoming milky or green with algae due to the low sanitizing ability of the combined chlorine.

Testing for combined chlorine in pool water

All good chlorine test kits and pool test strips allow you to determine free chlorine as well as total chlorine. Combined chlorine is calculated from these values as follows:

combined chlorine = total chlorine - free chlorine

The combined chlorine value should never exceed 50% of the free chlorine value and should ideally be as close to zero as possible.

Some cheaper test kits that use liquid reagents (drops) offer one value for the chlorine test. If the reagent bottle is marked "OTO" then you are only testing total chlorine and should consider a better test kit.

Destroying combined chlorine compounds

A shock treatment using either chlorine or a non-chlorine sanitizer will ensure the destruction of the nitrogen compound combined with the chlorine. The pungent smell disappears and the free chlorine level goes up providing complete sanitization of the pool water.

Pool water chemistry formulae - chloramines

  1. HOCl + NH3 = NH2Cl + H2O
    hypochlorous acid + ammonia = monochloramine + water
  2. NH2Cl + NH3 = NHCl2 + H2O
    monochloramine + ammonia = dichloramine + water
  3. NHCl2 + NH3 = NCl3 + H2O
    dichloramine + ammonia = trichloramine + water


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