Spotty problem: Spot etching, seen here near the waterline tiling, is a common symptom of water with low calcium hardness, low carbonate alkalinity, low total dissolved solids and/or low pH. In certain cases, it may also be a symptom of poorly mixed plaster or improper plastering practices.
Etching issues: The photo on the left provides a closer look at the distinctive deterioration that gives spot etching its name. Most of these spots range in size from about the diameter of a dime to that of a quarter — but in more severe cases, they may grow much larger. The photo above right shows the discoloration spot etching can produce when combined with metals or other chemicals in the water. If not treated immediately, such stains may become permanent.
Scaled up:Calcium scaling may be caused by high calcium hardness, carbonate alkalinity, total dissolved solids and/or pH. Though scaling reflects a mineral accumulation atop the pool surface, and thus tends to cause less permanent damage than etching does, it should still be avoided.
Scale stain: In the photo above, scaling can be seen around the seating shelf of the spa. Not unlike spot etching, scaling may result in stains when combined with metals or other waterborne chemicals. However, when staining on scale is removed, it sometimes reveals a strong, clean surface underneath.