Calcium hardness
Plaster wants 200–400 ppm calcium. How to raise it with calcium chloride, and why it only comes down by dilution.
Plaster, pebble and quartz finishes want calcium hardness of 200–400 ppm[1]. Vinyl and fiberglass don't need a minimum, but high calcium still scales.
- Raise CH 10 ppm in 10,000 gal: 1.2 lb of 77% calcium chloride (0.9 lb of 100% anhydrous)[1]
- Lower CH: drain and refill with softer water. Evaporation in hot climates pushes CH up all summer.
Read CH together with the LSI, not on its own.