Why does the water turn colors, and why do stains occur?

If there are metals dissolved in the water, the addition of shock products can turn the water colors and/or stain the pool surfaces because they oxidize the metals. The main types of metals found in pool water are iron and copper:

• Iron is often present in the fill water. It will give the water a greenish or yellow cast, then will turn rust colors. This generally occurs in the spring when opening the pool, as a lot of fresh tap water is addded, or if the pool is operated with the pH too low (<7) for a long time. Low pH will lead to corrosion of the equipment and fixtures.
   
• Copper can bre present in the pool water due to corrosive water (low pH) or if copper based algaecides are overdosed. Copper generally gives the water a greenish or blue cast. When dissolved copper is oxidized it will usually form a black stain on the pool surfaces. Chlorine will oxidize the metals in the water and result in colored water and/or stains. Operating the pump/filter system continuously will filter out these fine particles of oxidized metals and may help prevent staining. If the water has color when you are opening for the season or after adding a lof of fill water, take a sample to your Sustain Authorized Dealer and check for metals content. Use a metal removed prior to shocking the pool and circulate continuously.

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