Check the listing for details. SpaGuard Spa Calcium Hardness Increaser 12 oz - 12 Pack. Condition: New. Listed at 95.88 USD. SpaGuard's Spa Calcium Hardness Increaser is the perfect solution for spa owners to increase their calcium hardness levels easily and effectively. This granular formula is simple to use and helps boost calcium hardness to a safe level, preventing extensive corrosion of the spa's plumbing, jets, fixtures, and tub surfaces that can occur with low calcium levels. By gradually raising the calcium levels, this product ensures that you don't end up with too much calcium, which can lead to scale build-up and cloudy water. Maintaining optimal calcium hardness levels between 200-400 ppm is crucial for preventing corrosion, as anything below 100 ppm can cause damage to your spa. Product Feautures: 1 tbs. per 100 gallons raises the total hardness 25 parts per million Prevents surface etching due to low calcium hardness Helps prevent equipment and spa surface corrosion and damage