Pooling the acid has the opposite effect. A very important component of water balance, alkalinity should be maintained in the 80-120 ppm range. Levels should be tested weekly. It is a combination of carbonate ions, a part of Total Alkalinity and Calcium, a part of the Calcium Hardness level. The test for Calcium Hardness is a measure of how hard or soft the water is.
Hard water can have high levels of calcium and magnesium.
If these levels are too high, the water becomes saturated and will throw off excess particles out of solution, which then seek to deposit themselves on almost any surface inside the pool. This is calcium carbonate scale, a whitish, crystallized rough spot. If the levels are too low, the water is under saturated. The water becomes aggressive as it attempts to obtain the calcium it needs. Such soft water will actually corrode surfaces inside the pool which contain calcium and other minerals to maintain its hardness demand.