pH is a measurement of how acidic (below 7.0) or basic (above 7.0) – your hot tub water is. Alkalinity is a measurement of the amount of carbonates and bicarbonates in the water, which acts as a buffer to help stabilize pH. When pH is LOW (below 7.0), the water becomes corrosive to seals, gaskets and plastics. When pH is HIGH, the water can produce scale, leading to cloudy spa water or deposits of calcium on surfaces and inside pipes.