Calcium Scale
Calcium scale forms on pool surfaces due to very hard and out-of-balance pool water. Calcium scale is usually uniform and covers both plaster and pebbles in a pool. Calcium scale usually feels rough, like sandpaper, on the pool surfaces.
Calcium scale can occur on plaster, vinyl liner, or fiberglass pool surfaces.
Calcium scale is normally from calcium carbonate but can be from calcium sulfate (CaSO4). Aqua Magazine:The Mystery of the Pointed Crystals describes a calcium sulfate scale situation. Orenda Understanding Calcium Sulfate Scale Crystals further describes calcium sulfate scaling and solutions for it.
Calcium phosphate can also form scale and we rarely see that in pools.
It is important to identify the type of calcium scaling to know how to treat it. Calcium carbonate will fizz up in acid, while the other two either don't react at all or just slowly dissolve. By testing the calcium level and calculating the waters CSI as well as testing for sulfates and phosphates you can identify which chemicals are unusually high.
Calcium scale is different then waterline scale on tiles, evaporative scale on surfaces outside of the water, efflorescence, or calcium nodules.
