Calcium Hardness

Calcium Hardness

Calcium Hardness

The sum of all the calcium dissolved in water is referred to as the calcium hardness. Calcium is important since high levels are unstable and become even more unstable if the pH or the total alkalinity rise above the normal levels. These imbalances can result in cloudy water and/or scale. In addition, calcium does not like warm water. As water temperature rises, calcium becomes more likely to precipitate out of solution. Calcium is actually more soluble in cold water, which is why scaling of heater equipment is so common.

With all of the difficulties calcium can cause, it would seem logical to use soft water in filling a pool. However, this is not the case! While high calcium levels can cause problems with cloudy water and scale, soft or low-calcium water is also of concern. Such water is aggressive and will actually remove calcium from plaster in order to satisfy its need for the mineral. If the pool is vinyl or fiberglass, the low calcium water will actually attack metal fittings and heat exchangers resulting in destruction of the fittings or pinhole leaks in the heater. When such corrosion occurs, it is also common for stains to appear on pool surfaces.  It will also damage the vinyl or fiberglass surface you may have.

Testing the Water

Calcium content is best in the range of 100-400 ppm and is water temperature dependent. Unlike pH or total alkalinity, however, both of which can be raised or lowered with reasonable ease, calcium levels cannot.

Adding a hardness increaser to the water easily raises calcium levels. Conversely, there is no simple chemical addition that can be made that will reduce calcium hardness. The only way to reduce calcium hardness levels in pool water is through dilution with water of a lesser hardness. Over time, calcium hardness will naturally increase in pool water due to evaporation and possibly other factors unless the pool water is regularly diluted.

While it may be difficult to reduce calcium hardness, it is possible to control it so that a potential problem such as cloudy water or scale formation is prevented. The best way to minimize the effect of high calcium levels is through the use of a sequestering agent. A sequestering agent is a compound that, when added to water, will chemically bond with calcium and other minerals to make them, in a sense, more soluble. This means that calcium will still be present, but in a form that is less likely to cloud water or form scale if the pH or other factors get out of balance. In addition, since calcium will still be in the water, you will not have the corrosion problems you would otherwise experience with soft water. A further advantage is that elevated levels of calcium (over 400 ppm) can be tolerated without constant need for dilution. This becomes especially important when the pool is located in hard water areas or calcium-based chlorine sources are used.  A sequestering agent should be a part of your regular chemical maintenance program.

When dealing with calcium harness issues in your pool, it is suggested that your first line of defense is your local pool professional.  They can prescribe what is best for your pool to take care of and prevent any problem that can arise.


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