Calcium hardness problems

Pool water problem - calcium hardness

Total hardness in swimming pools is a measure of all the dissolved minerals such as calcium, magnesium and sodium. For practical purposes we usually use calcium hardness as a reference in pool water chemistry.

The recommended level for calcium hardness is 200 - 400 ppm, and both high and low levels result in swimming pool problems.

Low calcium hardness

Low calcium hardness results in corrosive water. The plaster surfaces or tile grouting softens and erodes, metal equipment and accessories oxidize and rust quickly, and the water becomes aggressive. This can lead to staining of the pool's surfaces as well as an eventual need for resurfacing.

Increase low calcium hardness

The calcium hardness level can simply be increased through the addition of calcium chloride or any commercial calcium increaser (which contains CaCl).

Alternatively, in swimming pools that suffer constantly of low hardness due to the quality of the fill water, calcium hypochlorite could be the chlorine of choice. This chlorine adds calcium to the pool water with each addition keeping the level up. Care must be taken to test Conditioner a couple of times a year as this chlorine (65% - 70% CHC) does not contain conditioner in its formulation.

High calcium hardness

High calcium hardness results in scale formation on the pool surfaces as well as scaling in the pipes, plumbing and filter. In extreme cases the water becomes dull and cloudy with the calcium precipitating out into the water rather than onto a surface. High calcium levels will also irritate swimmers, causing sore eyes in particular.

Reduce high calcium hardness

If the calcium is a result of pool chemicals, draining some or all of the pool water will lower the calcium hardness level. If the cause is the fill water, commercial hardness reducers or chelating agents will bond with the calcium to keep it trapped in solution

The Pool Wizard and high calcium hardness

One of the "side effects" of the Pool Wizard is to isolate calcium. In practice and in field tests, we have found that despite adverse conditions, pools tend not to scale with the Pool Wizard. We have also observed that existing scale softens and erodes in the presence of the Pool Wizard minerals. Light brushing can then easily loosen any unsightly scaling.


Zeolites, and clinoptilolite in particular, reduce pool water hardness when used as a filter medium in sand filters. They achieve this by ion exchange and adsorption of the calcium molecules. Regeneration with salt flushes the calcium out of the zeolite and it can then continue to remove excess calcium.


Tried and trusted since 1983


Pool Wizard will help most common pool water problems