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.
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.
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