Measuring calcium ion (Ca+2) concentration in water is refered as calcium hardness. Calcium carbonate expressed as CaCO3 which causes hardness in water. If the level is calcium is low then it is called as soft water and if the level of calcium is high then it causes hardness in water also refered as calcium hardness which lead to calcium deposition in water.
For example in pool water if calcium carbonate level is low it will cause corrosion and also cause the deposition of other minerals, if calcium carbonate level is high it causes deposition of calcium on pool surface and other pool equipment.
The calcium level should be maintained (measured in PPM), in pool it has to be between 200 and 400 ppm.
If calcium level is low then it is compensated from calcium chloride thus preventing corrosion.
For physical and chemical properties please refer provided link.