Why is my pool cloudy/milky?

There are four possible causes – your test kit or pool professional will give you the best idea as to which is the most likely.

  • Fine suspended particles floating in the water can lead to a milky white discoloration. This is likley due to a precipitation of dissolved hardness salts as result of high pH or high total alkalinity, or both. (Precipitation is a process where dissolved minerals become transformed into very small solid particles).
    • Lower the pH or alkalinity using dry acid.
    • To correct pH, add dry acid at a rate of 1 pound per 10,000 gallons per day  until correct level is attained.
    • To correct alkalinity, the dose should be doubled.

It is important to add the acid a little at a time because both pH and Alkailinty will be lowered by dry acid. And always treat the Alkalinity FIRST.


  • Build up of dirt and bather pollution due to insufficient chlorine or poor filtration
    • Backwash filter, then superchlorinate by adding an unstabilized chlorine such as sodium hypochlorite or calcium hypochlorite to raise the free chlorine to 10ppm.
    • Add a clarifier to polish the water.
  • The effectiveness of the chlorine has been reduced in pools using stabilized chlorine because the water is over-stabilized, meaning the levels of stabilizer (cyanuric acid) are too high. This prolongs the time it takes to kill organisms which can proliferate and lead to haziness in the water.
    • Replace some of the pool water by draining to waste (or carrying out an extra large backwash), then top up with fresh water. This will lower levels of stabilizer.
    • Superchlorinate to 10ppm using the products recommended above.
  • The filter is blocked or is ineffective
    • Check sand and replace if necessary. Your pool professional should be called in if you do not feel you are able to replace filter sand.
    • Sand particles can become coated with calcium in some circumstances, especially in hard water areas. If the filter is not blocked and seems all in order in all other respects, treat with a filter cleanser to increase the filtration properties the sand.

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