Superchlorination or Shocking

chemicals for superchlorination

- AKA ‘Shock dosing’

Warm water presents ideal conditions for algae to establish themselves in your pool and the slightest inattention on your part can result in a nasty, unhealthy green mess that can take the untutored days or even weeks of hot, sweaty labour to clean up

  • An algae bloom, especially if it is left untreated for a few days, is very bad news indeed
  • As algae proliferates it strips carbon dioxide from the water
  • The pH of the water then rises and the Sanitizing Chemicals become less effective – allowing the algae to flourish – which raise the pH – which makes the chemicals even less effective - which allows the algae to grow even faster. . .   you can probably guess how this might continue . . .?
  • When pH reaches 8.6 the minerals dissolved in the water precipitate out (the water turns milky) - coating the tiles, the plumbing and the filter media with lime-scale
  • The extra minerals now available in the water provide building materials for more and more algae and the process accelerates
  • The best defence against algae bloom is routine, systematic Superchlorination - the secret ‘right-hook’ of the Pool Professional
  • Superchlorination or ‘shock dosing’ refers to the addition to the water of anything that will remove or destroy ammonia and nitrogen compounds by oxidation - traditionally this has been a Chlorine compound
  • Organic matter and ammonia compounds can get into a pool from many sources
  • Swimmers and bathers are major contributors with their bodies giving off skin flakes, mucus, saliva, sweat, urine and faecal matter
  • Dust, fertilisers, algae, leaves, twigs, certain water-treatment chemicals and rain also introduce contaminants into the water
  • (Here’s one unusual way that a pool can become contaminatedcontaminated)

Instructions for Superchlorination

  • High Chlorine levels can weaken and destroy a pool-cover very quickly, therefore keep the cover off until Chlorine has returned to normal levels of 1-3ppm
  • Add the chemical to the water at the jets to promote rapid mixing
  • Run the pump for 4 hours to circulate the superchlorination chemicals
  • The pool is out of action for twelve hours after superchlorination; therefore you apply it when you have finished using the pool for the day, secure in the knowledge that the water will be sanitized and safe the next day
  • If you want to use the pool sooner than after 12 hours, you can add Sodium Thiosulphate to reduce high levels of Chlorine
  • Liquid chlorine has a pH of around 11.6, so this amount of Chlorine will alter the water balance and the pH will rise
  • To counteract this rise add 1 litre of liquid acid at the same time
  • Add the acid at the Jets with the pump running but wait a few minutes after adding the Sodium Hypochlorite to allow it to disperse first
  • In addition to regular fortnightly treatments, carry out superchlorination after a thunderstorm or if the pool is subjected to unusually heavy pollution e.g. a child having an ‘accident’ in the water
  • Check the water chemistry, and add chemicals, little and often for best results
  • Always wash your hands immediately after handling pool chemicals

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Ken Walker - MyPoolGuru©