Dangerous combinations: Changing chemical conditions can create some bizarre colors and textures on plaster surfaces. In this pool, a combination of copper and cyanuric acid produced purplish crystals that coated the pool’s walls and floor.
Warning signs: Even subtle stains may indicate a serious problem, so it pays to investigate them thoroughly. The bit of copper staining shown here could be caused by oxidized copper in the source water, which has the potential to stain all plaster surfaces if left untreated for a week or so.
Thorough testing: To ensure you’re getting a clear sense of a pool’s chemical conditions, it’s important to test water in several areas of the pool, and compare your results. Triple-checking your conclusions with multiple types of tests will ensure that you present the homeowner with the most accurate analysis possible.