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There are 6 reasons why your pool water may be cloudy. They are:

  • High pH
  • High Calcium Levels
  • Low water flow
  • Dirty filter
  • High Phosphates
  • Time to shock chlorinate

Our technician visited a green pool last year that had five times the normal chlorine level and was still green! Why?  The pH of the water was so high that the chlorine was prevented from working and so it was not able to clear the pool.”

High pH

If the pH of your pool water is high, the effectiveness (or killing power) of pool chlorine is greatly reduced. This may cause the water to appear cloudy.  The orange line on the graph shows that when the pH is at 6.5, chlorine is 91% effective. It also shows that when the pH is 8.5, chlorine is only 9% effective.  In short, high pH “locks up” chlorine so check the pH regularly!

kill rate of chlorine

Low Water flow

It is vital that the pump you use is the correct size for your swimming pool. If it’s too small, then there will be insufficient water flow to filter the water properly.  Too large, and the high flow through the filter can cause the fine sand to be blown through the pipework and into your pool. Also, cloudiness may be caused from inadequate filtering time each day, even if your pump is the correct size. This means that there isn’t enough pumping time for all the water in the pool to be properly filtered and chlorinated.

High Phosphates

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 dirt can also play a role in increasing phosphates which can lead to cloudy water.  A good information article about the facts and myths surrounding phosphates can be found here.

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.
  • If the water is very dirty so that you can’t see the bottom, try using a flocculent to clear the murky water.  This will gather, or ‘flock’, the dirt in the water and bring them to the bottom of the pool where they can be then easily removed.
  • A skimmer basket sock helps filter finer particles which can also help reduce the amount of debris entering the filter. Using a sock will mean your filter stays cleaner for longer

High Calcium Levels

High calcium hardness levels can lead to cloudy pool water.  To check your calcium levels, take a water sample to your local pool shop.  They can test your calcium hardness levels for you. According to Australian Standards (1926.3), concrete pools require a calcium hardness level between 100-300 ppm. For fibreglass pools please contact your pool manufacturer to obtain the recommended levels for your pool.

Backwashing Dirty Filter

Most sand filters should be backwashed every 2 weeks during winter and every week during summer.  Cartridge filters should be cleaned at the same time intervals.  However, backwashing more frequently than this can lead to excessive sand loss, cloudy water and poor filtration.  Changing the sand in your filter every 7 years can be a great idea.  Old sand filters with the original sand inside will often have huge lumps of solidified sand that has bonded together inside the filter.  This means that the water is simply bypassing the sand and re-entering the pool.

Shock Chlorination – does your pool turn green several times a year?  Here’s why.

Regular shocking will remove the ‘dead’ chlorine (chloramines) from your pool and kill off most algae growth.  These chloramines ‘bind up’ the free chlorine and significantly reduce its effectiveness. Because of this, your pool water can have plenty of chlorine but still be green and stay green.  To shock chlorinate properly, most pools typically need at least 20 litres of chlorine. This should be done every 6 months.  Your pool shop can help you determine the right amount of chlorine needed to properly shock your pool.  Shocking at the beginning and the end of the swimming season is a great idea.

Final thoughts

Cloudy water is common during late Spring when the weather and water starts to warm up.  If the chlorination system remains on winter mode, then this can lead to low chlorine levels in the warming pool water which causes cloudiness.  As a rule, most pool pumps and chlorinators need to run for 4 hours a day in winter and 8 hours a day in summer to keep the water clear and safe.

References / Credits

dirty sand filter
Old sand filters with the original sand inside which has since partially solidifed
green pool
Pool water can have plenty of chlorine but still be green