What is it?

Copper may erode from the spa’s heating system and dissolve into the water due to low pH, low total alkalinity and low calcium hardness. This can show up as green or greenish-blue water. In addition, the source or make-up water may also have high levels of metal such as iron copper or manganese. Changes in water balance (usually from an increase in pH or application of a shock product) can cause the metals to become insoluble and allow them to drop onto the spa surface, resulting in staining.

To remove metal stains:

To prevent metal stains: