Leslie's - Hardness Plus for Calcium Hardness, 4 lbs.

The calcium hardness level in a pool does not increase rapidly, but it is good practice to check the calcium hardness every month. Adding 1.25 pounds of hardness plus to 10,000 gallons of water will raise the calcium hardness by 10 ppm. **The minimum level of Calcium Hardness is 150 ppm.

Signs of Low Calcium Hardness in Your Pool

• Metal Corrosion: When calcium levels are too low, the corrosive nature of soft water can cause it to go after the metals in your pool, including handrails, ladders and equipment. In addition, Calcium Hardness often goes hand in hand with other aspects of pool water chemistry, such as Total Alkalinity or pH.
• Concrete and Plaster Corrosion: As pool water becomes more corrosive, it attempts to balance itself by leaching calcium from plaster, concrete, grout, tiling, or other pool surfaces. This causes pitting and delaminating, which essentially means the corrosive pool water eats away at the structure of your pool.
• Foamy Water: Soft water increases the likelihood of issues with unsightly pool water foam.