Calcium Hardness
Calcium Hardness is a measurement of the level of calcium in the water, and may be
referred to as “water hardness”. It is measured in parts per million, or ppm.
This is often one of the most ignored parameters, yet just as important as the others.
The hardness of your pool water is very important in controlling scale and the corrosive
effects of water.
A low calcium level may cause pool water to become corrosive, even if the pH is within the
recommended range. Left unchecked this can damage the pool interior finish, and the
equipment.
A high calcium level may cause the pool water to deposit scale even if the pH is within the
recommended range. Scale build up on the pool surfaces can be unsightly and difficult to
remove, and it will also build up inside the pool equipment.
Scale can be particularly harmful to heating equipment as it can severely reduce the
efficiency of a heat exchange.
Scale can also build up on the plates inside your salt chlorinator cell. If left unchecked this
will damage the cell, and also risk voiding your warranty if it is not cleaned regularly.
Pool Lab Chlorinator cells feature a 'self-cleaning' design, but this will only work if your pH,
Total Alkalinity and Calcium Hardness parameters are within an acceptable range.
Generally a calcium hardness level between 100 – 200 ppm is recommended for most
pools. Consult your local pool professionals or your pool documentation for the
recommended range for your pool.
The calcium hardness level can be raised by the addition of calcium chloride to the water.
Pool shops usually referred to this as “Hardness Increaser” or similar. Always test the
water first before adding this as some water sources may already have significant
hardness depending on where it comes from.
In some cases the initial calcium hardness may be well above the recommended range,
and in these cases we recommend using the Langlier Index to determine an ideal pH
value that will prevent this water from scaling. See next page.
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