LaMotte Pool Manager Water Quality Handbook - Manual (Page 19)

Calcium Hardness
What is Calcium Hardness?
Calcium hardness refers to the level of calcium dissolved
in water. If the water has an abundance of calcium, the
water is described as “hard”; water with a low content is
described as “soft.” The most common source of calcium
in pools is fill water, especially if the source or aquifer
contains high calcium. When pool water is low in
calcium content, calcium may dissolve from plaster
surfaces. The term “total hardness” refers to both the
calcium and the magnesium content of the water. Do
not confuse total hardness test results with those for
calcium hardness.
Why do we test Calcium Hardness?
Testing calcium hardness evaluates
the pool water’s aggressive, or
saturated nature. Water is naturally
aggressive and is known as “the
universal solvent.”
In pool water it is important to
evaluate the level of calcium
hardness since water has a natural
tendency to dissolve certain
minerals that are a component of
the pool surfaces. If the water
contains too many minerals it
becomes saturated and the calcium
will begin to fall out of the water,
settle around the pool, and leave
noticeable crusty, white deposits.
These deposits are called scale and
can be seen on pool parts and walls.
Scale can clog filters, heaters, and
plumbing fixtures—leading to poor
water circulation and costly repairs.
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Hard Water
stains dishes and clothes
Soft water
leaves items clean and clear