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Occasionally pool water can lack clarity, becoming milky or cloudy in appearance. There are several factors that can cause cloudy water.

  • A pump size that is too small can lead to poor water flow resulting in low water circulation.  A pump size that is too large can lead to very high flow through the filter.  This can lead to fine debris being forced out through the filter and back into the pool.  If your pump is the correct size, cloudiness may be caused from limited filtering time each day.  Insufficient filtering does not allow enough time for all the water in the pool to be properly cycled and filtered.  Cloudy water is common during late Spring when the weather and water starts to warm up.  If the chlorination system remains on winter mode this can lead to low chlorine levels in the warmer pool water which causes cloudiness. Insufficient vacuuming and brushing can also contribute to the problem, but this is a less common cause.  Finally, large solid lumps of sand in old clogged sand filters are a very common cause of murky water and poor filtration.

Possible Solutions

  •  Run the pump and filter for longer periods each day to increase water circulation and filtration.  Make sure you are regularly cleaning and backwashing the filter properly.  If you have a sand filter, be sure that the sand is changed every 5 years so it can filter efficiently.As mentioned, correct pump sizing is also important because a pump that is too strong will force filtered debris back into the pool!  On the other hand, a pump that is too weak will not allow for proper circulation leading to cloudy water and algae growth.  In some cases, the first sign that your pool may turn green with an algae bloom is the water will first become cloudy.
  • Sometimes cloudy water has little to do with the size or cleanliness of your pool equipment or filter.  Bird and duck droppings, leaves, pollen and excessive dust and dirt can also play a role in creating cloudy water.  Pools near construction/renovation sites are often difficult to keep clean and clear.  Also, very high total alkalinity can cause water to become more cloudy than usual because of chemical imbalance.

Possible Solutions

  • There are three solutions for murky water problems in this category.  First, a clarifier will gather the water borne particles into larger sizes that can be filtered out.  This process clears the water without any further action.  Second, if the water is very cloudy, try using a flocculent to clear the murky water.  These products gather or ‘flock’ the dirt and water borne contaminates and drag them to the bottom of the pool.  This will then clear the water and drop the sediment to the bottom of the pool where it can be vacuumed to waste. It is important that this last step be done according to directions as leaving the material at the bottom of the pool could result in surface damage.  Finally, a skimmer sock to the leaf basket helps filter and remove finer particles.  .
  • While most of the reasons for cloudy water are outlined above, there are occasions when poor water chemistry can be the cause.  If the pH and total alkalinity of the water become too high, then this can lead to the water appearing dull and your sanitiser becoming less effective.  It is unusual to find a green cloudy pool that is properly balanced and has a normal chlorine level. Remember, the effectiveness of chlorine is reduced when the pH is very high.  The orange line on the graph to the right shows that when the pH is at 6.5 the chlorine is 91% effective.  The same graph also shows that when the pH is 8.5, chlorine is only 9% effective.  In short, high pH wipes out the effectiveness or killing power of chlorine even when there are high chlorine levels present in the water.   High calcium hardness (CA) can also cause water to appear murky during the summer months. 

Possible Solutions

  • If it has been some time since you shocked your pool water with chlorine, then it may be a good idea to do take this step.  Regular shocking will revitalise the chlorine, remove (oxidize) unwanted waste and kill off any algae growth.  Remember, if your pool water is properly balanced then it is unlikely that bad chemistry is to blame for cloudy water.
Cloudy  Water 5
Cloudy  Water 6

The orange line shows that higher pH levels destroy

the killing power (or effectiveness) of chlorine.