Copper staining in pools

Copper staining in pool interiors is generally caused by four main products.  These include copper sulphate blocks, copper-based algaecides, contaminated pool salt or chlorine-free pools that use copper and silver to sanitize water. Copper stains will often appear when the pool water is out of balance and the pH is too high. Many people first notice copper stains when they remove the pool cover in Spring. Some pool owners decide to not take care of the pool water during winter which is when the worst of the staining occurs.

Causes of copper staining in pools

  • Copper sulphate (blue algae blocks)
  • Copper based algaecides
  • Chlorine free pool systems
  • Contaminated pool salt
Remember that the best way to prevent staining from these products listed above is to test and balance the water regularly.  If the water is maintained then even if small amounts of copper are present in the water then the copper will not usually stain the pool surface.  This is because balanced water can suspend or hold copper in solution.  

“Copper staining can be green, teal or black depending on the age of the stain and the chlorine levels in the pool water.”

copper staining in pool


     Copper staining reacts (oxidizes) in the presence of chlorine by turning a dark colour

Pool copper stains can look green like algae

Be careful when taking advice from some pool technicians about copper staining in swimming pools. For instance, many pool owners often mistake copper staining for a green algae. In these cases, the pool owners will buy treatments or huge amounts of chlorine which makes the copper staining more obvious. This is because the chlorine oxidizes the copper on the pool surface which turns it dark grey or black . There is more information on staining types here.

Remove copper from pool water

There are various ways to remove copper from pool water. The most common way is to add a chelating agent to the water. This gathers the copper ions together which makes them easier to capture in the filter. Generally these products contain phosphoric acids as the primary ingredient. Consequently, this will mean that you will need to remove phosphates from your pool after using these products. Also, these products are readily available in most pool shops.

The other method used to remove copper is to drain the entire swimming pool.  This is not required in most cases unless the copper has reached extreme levels.  It would be a good idea to check with your local pool before making this decision.

Remember, that these products will not remove copper staining in pool surfaces. In other words, they remove copper from the water, not from the pool surfaces. Many people buy these products expecting to remove the stains only to be disappointed. They may help with very mild staining but most often the stains are still left behind.

remove metals from pool water


This is one of many products that remove metals from swimming pool water.

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