Hypochlorous Acid

- when Chlorine in its various forms is added to the water it produces Hypochlorous Acid - the chemical formula for which is HOCl 3D molecule hypochlorous acid(Hydrogen+Oxygen+Chlorine)

  • Hypochlorous Acid controls bacteria and algae and also oxidizes organic wastes
  • Hypochlorous Acid is a very weak acid and therefore not harmful to people
  • HOCl dissociates (splits up) in water like this: - HOCl <===> H+ + OCl- (hypochlorite ion)
  • HOCl reacts with bacteria and organics and is a very effective sanitizer
  • OCl- reacts with ammonia (NH3) and is an extremely strong oxidizer
  • HOCl reacts with sunlight and is destroyed by it
  • Therefore Cyanuric Acid (CYA) is maintained in the pool at a concentration of 30-50ppm, to protect the Hypochlorous Acid
  • HOCl exists in a killing form (HOCl) and as a strong oxidizer (OCl-)
  • The pH of water determines the proportions of HOCl, H+ and OCl- that are produced
  • The pH of the water is therefore very important
  • Chlorine works most efficiently when the pH of the water is at, or close to, 7.4
  • At low pH Chlorine is used up very quickly
  • At a high pH Chlorine doesn't produce very much Hypochlorous Acid - it is mostly in the form H+ and OCl- (plenty of oxidizer but not much sanitizer)
  • Pools kept at higher pH values have more problems with algae and bacteria, so the Chlorine level must be raised to compensate for this
  • Chlorine as Hypochlorous Acid (HOCl) is needed for sanitizing pools
  • Chlorine as (OCl-) is needed for oxidization of pollutants
  • Hypochlorous Acid is reduced to inactive chloride ion when it has completed its task
  • The reaction of HOCl with ammonia produces a series of chlorine-like odorous, irritating compounds called ‘chloramines’ or ‘combined chlorine’
  • Combined Chlorine is a very poor sanitizer
  • Chloramines irritate eyes, skin and mucous membranes and are often confused with Chlorine because they smell strongly
  • Free available Chlorine at levels up to 20 ppm has no detectable taste or odour and causes little or no irritation to  eyes, skin and mucous membranes
  • This level of 20ppm is not safe for swimming, however, and pools should be kept below 5ppm, ideally in the range 1-3ppm

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Ken Walker - MyPoolGuru©