Stains that are blueish green in color is primarily caused by the corrosion of copper within the plumbing. These stains are most noticeable on sinks tubs and toilets but can occur on pipes as well.
The corrosion of pipes and plumbing fixtures can cause a number of problems with your water. Corrosion starts at the surface and moves inward. A common cause of this is acidic water or low pH. Acidity in water can have an adverse effect on the taste and quality of your water.
There are a few options for raising the pH of your water: