Costa Rica Pools & ConstructionGlen BainPool Care Basics

What Causes the Different Colored Stains in My Pool?

 By Glen Bains 

Minerals and other substances find their way into every pool. Iron, calcium and copper exist naturally in source water, and can be prevalent in well water. While other materials can stain plaster and vinyl just as easily – sources include organic matter such as leaves, and excessive oxidizer – dissolved minerals remain one of the most common staining culprits. In an ideal world, pools would never suffer from stains because their perfect water balance would hold metals in solution all the time. In reality, though, pH and alkalinity can drift and calcium levels can climb, leading minerals to fall out of solution, or precipitate, and stain. The key is maintaining a good chemical balance to avoid the ups and downs, but sometimes change is impossible to avoid. To combat this problem, try to keep your chemicals balanced at all times but in between our service calls, change can occur. 

The following is a list of minerals and the color of their stain:

  • Calcium – usually white crystals adhering to the pool plaster.
  • Cobalt – fiberglass shells – red, blue, gray and black.
  • Copper – Blue, green, black, teal and dark red.
  • Iron – Dark red, brown, black, gray and green.
  • Manganese – Pink, red and black.

Many of these stains can be removed with acid washing the pool plaster or stained area. Success really depends on how deep the stain goes, as acid washing removes a small amount of plaster, grout or cement. 

If you need help with your pool please contact Costa Rica Pools at 506-2777-1700 or 506-2643-3227 , or by email at [email protected] or

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