Calcium Hardness

Ideal range: 200 – 400 ppm

calciumWater that contains little or no calcium or magnesium is called soft. Water that contains high levels of calcium and magnesium salts is called hard as it consumes soap and makes it “hard” to form suds. In wash water the minerals combine with soap to form a grey insoluble curd-like scum, making cleaning less effective yet more expensive. With the advent of synthetic detergents, this problem has improved; however, for home and some industrial processes, hard water is often “softened” before use by water softeners that remove all of these minerals.

In laundry applications, the goal is to remove calcium/magnesium from water. In pools, magnesium does not form scale and interest is focused only on calcium. Pools having too much calcium may scale, but pool water entirely deprived of calcium becomes aggressive and seeks to dissolve calcium into the water from contact surfaces, such as grouting or concrete. High hardness can be reduced by partially draining the pool and refilling with fresh water of lower hardness.

THE EFFECTS OF HIGH AND LOW HARDNESS                                                Specifically, water with high calcium hardness gets cloudy unless the alkalinity and/or pH are low enough to compensate. As mentioned, the excess calcium carbonate will precipitate as crusty, grayish white scale on surfaces, piping, and equipment. It’s unsightly, can cause abrasions on users and snag bathing suits, and makes a good anchor for microorganisms. It will clog filters. When it builds up in piping, circulation is reduced and pressure increases. Scaling is an especially acute problem in heaters because calcium’s solubility is inversely proportional to temperature:  as temperature increases, less calcium is able to stay dissolved. Scale on the pipes or coils acts as an insulator, slowing heat transfer. This makes it more expensive to heat the water. Over time, thick scale will cause a heater to fail.

Water with low calcium hardness will seek more by dissolving it from surfaces it comes in contact with that contain calcium, such as plaster, grout, and concrete decking. The late Dr. Neil Lowry, a well respected instructor in our industry, preferred to call water with low calcium hardness “aggressive” rather than “corrosive” because the latter term implies the destruction of metals. He would point out that copper water pipes in homes equipped with water softeners last for decades! The corrosiveness of unbalanced water, he would tell his students, comes from poorly maintained alkalinity and pH.

Low Calcium Hardness:

  • corrosive wateretching of plaster
  • pitting of concrete
  • dissolving of grout
  • pitting of pool decks

High Calcium Hardness:

  • scaling water
  • white film/crusty deposits
  • plugged filters
  • reduced circulation
  • cloudy pool
  • heater inefficiency

CalcHardness scale