Natural Chemistry Spa Calcium Hardness Increaser boosts the calcium hardness level in your spa or hot tub, which is an important factor in overall spa health. Low calcium hardness levels can cause corrosion damage to spa surfaces, plumbing, and other equipment that can cost considerable money to repair. It also can cause eye and skin irritation for bathers. Spa Calcium Hardness Increaser prevents these problems by steadily raising the hardness level into the optimal range of 150 to 250 ppm, protecting spa equipment and making its water clear and comfortable. This product is made by Natural Chemistry, which has been an industry innovator in harnessing the power of natural compounds and enzymes to maintain pools and spas for almost 20 years.