Check the listing for details. Spa Essentials Calcium Hardness Increaser 12oz. Condition: New. Listed at 18.99 USD. Spa Essentials Calcium Hardness Increaser - 12oz Part # 325340000 Spa Essentials Calcium Hardness Increaser provides spa owners with an easy and effective way to increase their spa calcium hardness levels to problems that will affect the long-term life of their spas. Calcium Hardness Increaser raises and helps maintain the proper levels of calcium, which when imbalanced will cause corrosive damage to spa equipment, fixtures, and tub surfaces. This one-step treatment will make owning and enjoying a spa easier than ever. Product Dosage: 1 tsp per 100 gallons will raise hardness by 8 ppm Returns are not accepted on opened or used products and are subject to a 10% restocking fee. If you have any questions, please contact Clearview Fireplace and Patio. We would be happy to help!