Calcium hardness is the measurement of water to see if the water is soft or hard. When pool water calcium hardness levels are low, the water in the pool becomes aggressive because the water is undersaturated. When the hardness of the water is low, it can corrode fixtures or plaster pool walls that contain calcium. The ideal reading for calcium hardness in pool water is about 200 to 400 parts per million.
Test the water for calcium hardness using a test strip from the calcium hardness test kit. Dip the strip in the water on the deep end of the pool as far down in the water as you can reach.
Remove the strip from the water. Compare the color of the strip to the color chart in the kit. This tells you the hardness level in the water. If the level is below 200 ppm, you need to raise the level.
Measure out enough calcium chloride to raise the hardness level. Use 1 1/4 pounds of product per every 10,000 gallons of water if you need to raise the level 10 ppm. Use 2 1/2 pounds to raise the level 20 ppm, or use 6 1/4 pounds of product to raise the hardness level 50 ppm.
Fill a bucket with warm water. Add the calcium chloride to the water. Never add water to the compound. Allow the product to dissolve.
Start pouring the mixture into the deep end of the pool. Slowly walk around the deep end, pouring the mixture until it is all gone. Turn on the pool filter and let it run for at least six hours.
Retest the calcium level the next day. Assuming the level is correct, check the chlorine, pH and alkalinity levels and adjust if needed. Return the pool filter to its normal operation schedule.