Calcuium hardness measures the amount of Calcium Chloride in the water. This is not of great concern in a vynil lined pools like Intex models. However, if the hardness drops too low, there could begin to be some corrosive effects on pumping equipment, ladders, and metal frames.
In the unlikely event that Calcium hardness falls too low, purchase and add calcium chloride at a pool store. If calcium level is too high, the only way to lower it is by draining & replacing water.