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28th May 2020


Probable causes:

  • High pH and/or total alkalinity
  • Low free chlorine level
  • High stabiliser (cyanuric acid) level
  • Poor or inadequate filtration


Cloudy  Swimming Pool water could be due to a number of factors: high total alkalinity or pH which bring hardness salts out of solution, low free chlorine allowing a build-up of bacteria, poor filtration which is ineffective at removing particles suspended in the water, or the start of an algae bloom.

The use of a test kit or test strips may help to establish the most likely cause.

What you may need:

pH & Alkalinity Reducer – To correct high pH and/or alkalinity

Shock Chlorine – To shock chlorinate the pool

Coagulant – To clarify the pool water after killing the algae

Action to be taken:

  1. If due to high pH and/or alkalinity
  • The pH tells us whether the water is acid or alkaline and requires checking on a regular basis. It should be maintained in the range 7.2 – 7.6. If the pH is above 7.6, lower it by dosing pH & Alkalinity Reducer at a rate of 500g per 50m3 (11,000 gallons). With the circulation running, distribute around the pool, avoiding the skimmers. Do not dose it in one spot otherwise some alkalinity may be destroyed.
  • Alkalinity should be kept between 80 – 150mg/l (ppm). If necessary, it can also be reduced using pH & Alkalinity Reducer.


  1. If due to low free chlorine


  • NOTE: The free chlorine residual should be maintained within the ranges 2.0 – 4.0mg/l (ppm) for stabilised and 1.0 – 3.0 for unstabilised chlorine products, even when the pool is not in use. If you are using Chlorine Granules, you will need 90g per 50m3 (11,000 gallons) to provide 1mg/l (ppm) and 64g for Shock Granules.
  • Shock chlorinate the pool using Fi-Clor Superfast Superchlorinator. Add the contents of one entire 450g shock pot to 50m3 (11,000 gallons), or pro-rata* for other pool sizes. This will raise the chlorine level by approximately 7mg/l (ppm). Distribute the required quantity across the deep end of the pool with the pump running. *Approximately 64g per 50m3 (11,000 gallons) will increase the free chlorine by 1mg/l (ppm).

WARNING: Do not mix Fi-Clor Superfast products with any other types of chlorinating compounds (even other products in the Fi-Clor range) either in the dry state, or in the skimmer. Fire or explosion may result. If using with other products, dose them separately into different areas of the pool.


  1. If due to high stabiliser level


  • Stabiliser is essential in an outdoor pool but if you are using either stabilised chlorine granules, Maxi or Mini-Tabs (including multi-functional products), the stabiliser level may well increase depending on the level of water replacement.  The stabiliser level should be between 30-60mg/l, but ideally at the lower end of this range following a water replacement.


  1. If due to poor or inadequate filtration


  • It is good practice to have the quality of the filter media checked every 2 years. The correct depth of media is essential if your water is to remain free from small suspended particles.
  • Ask your dealer to check that there is a good flow of water being taken from the bottom drain of the pool.
  • The filter may be aided in the removal of very fine suspended particles by the use of a coagulant. To keep the water sparkling add a routine dose each week.