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How to clear up cloudy pool

These 6 steps will clear cloudy swimming pool water.

  • Test the water pH
  • Check your calcium hardness level
  • Make sure you have good water flow
  • Clean (or backwash) your pool filter
  • Check for high phosphates
  • Shock chlorinate the water if it has not been done recently

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 reduces the killing power of chlorine

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 can cause cloudy water

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 in pool water

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.  While high phosphates should be removed, an interesting article about the facts and myths surrounding phosphates can be found here.

There are three solutions for clearing cloudy water problems in this category.

  • First, a clarifier will gather the water borne particles together so they can be filtered out.  This process often clears the water completely.
  • If the pool water is very cloudy and you can’t see the bottom, try using a flocculent to clear the water.  This will gather, or ‘flock’, the particles in the water and bring them to the bottom of the pool so they can be removed.
  • A fine skimmer basket sock helps trap finer particles before they enter the main filter. Using a skimmer sock will keep your filter clean.

High Calcium Levels in pool water

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 a sand 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 lumps of solidified sand throughout the filter.  This means that any contaminates in the pool water are simply bypassing the lumps of sand and re-entering the pool.

How to shock chlorinate a swimming pool

First, start by testing your pool water to make sure the chemistry is in balance.  Remember, 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.  Finally, shock chlorinating at night will help the liquid chlorine to be protected from the UV light from the sun.

How to clear cloudy pool water

The best way to clear cloudy pool water is to run pool pumps and chlorinators for around 4 hours a day in winter and 8 hours a day in summer to keep the water clear and safe. It is common during late Spring when the weather and water starts to warm up for pool water to turn cloudy.  This is because the chlorination system may still be on winter mode (4 hrs per day) when the weather starts to warm up and this can lead to low chlorine levels.  This means that the warming pool water will have low chlorine levels that cause cloudiness in the water.

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