- what's that awful smell?3D chloramine molecule

  • Chlorine and Bromine combine with ammonia and Nitrogen compounds to form ‘-amines’.  
  • Chloramines smell bad, they are eye and body irritants and they are also poor disinfectants
  • Organic wastes build up and become sources of irritation
  • Bromamines do not have an odour problem and are as effective as free bromine for disinfection
  • Dealing with the problem of combined Chlorine requires testing the water to see how much of the Chlorine in the water is 'free' and how much is 'combined'
  • The commonly used Reagent test-kit will not perform this task.  It can only tell you the total Chlorine level and can't differentiate between free and combined Chlorine
  • However, a DPD test kit or a syringaldazine test strip will do the job
  • Chlorine reacts with Ammonia and destroys it.  When Chlorine is introduced into swimming pool water it instantly forms Hypochlorous Acid (HOCl or free Chlorine) which dissociates (splits up) into H+ and OCl-, the ratio of dissociation depends upon the pH of the water
  • The OCl- is a strong oxidizer and will oxidize the ammonia to form a combined Chlorine compound known as monochloramine (NH2Cl) and OH-
  • More Chlorine (as OCl-) is required to continue the oxidation of the Nitrogen or ammonia
  • If no more Chlorine was in the pool or added to it, the pool water would have a large amount of combined Chlorine as monochloramine rather than the desired free Chlorine
  • As more Chlorine is added, the monochloramine is now oxidized by the additional Chlorine as OCl- to form dichloramine (NHCl2 + another OH-)
  • The dichloramine is again oxidized by OCl- to form trichloramine (NCl3 + another OH-)
  • The trichloramine is unstable and breaks down to simple nitrogen and chlorine, thus completing breakpoint chlorination
  • Superchlorination to truly achieve the destruction of all organic waste can be very tricky
  • If insufficient Chlorine is added the combined Chlorine problem is only made worse. When this happens, eye burn and skin irritation are raised to very high and uncomfortable levels
  • If too much Chlorine is added, it may take days to drop to safe levels (less than 4 ppm) before bathing can be resumed
  • It takes 7.6 parts by weight of Chlorine to oxidize 1 part of ammonia. Other organics or products in the water will also consume some of the added chlorine so that 7.6 parts is not enough
  • 10 parts of Chlorine for each part of ammonia is generally accepted as being the required amount
  • Dirty and contaminated pools could take up to 25 parts or more of Chlorine
  • As a general rule of thumb, the addition of 10 times the combined Chlorine level will achieve breakpoint
  • So, if the water has 0.5ppm of combined Chlorine by test, you will need to add 5 ppm or more of Chlorine to destroy the combined Chlorine
  • Each commercial Chlorine product provides a different amount of available Chlorine when added to water, so read the instructions first
  • In a typical 50,000 litre (13,000 US Gal) pool it will take about 0.5 Kg or 1 pound of available Chlorine to achieve 10 parts per million

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Ken Walker - MyPoolGuru©