Calcium hardness in hot tubs must be maintained at 150 to 300 parts per million (ppm). If the calcium in the tub is high, it can cause cloudy pool water and scaling formations on the walls and fixtures. There are two ways to lower calcium hardness in hot tubs to meet the ideal range. Before you make any adjustments to the spa, however, you need to know how high the calcium hardness is.
Test the calcium hardness level of the water with a test strip from the calcium hardness test kit. Dip the strip into the water and pull it out. Place the strip next to the color chart that comes with the kit to see what the level is at and how much the calcium needs to be lowered.
Measure out 1 1/2 oz. of trisodium phosphate for every 1,000 gallons of water in the hot tub to lower the calcium hardness by 11 ppm. Pour in the trisodium phosphate as you walk around the hot tub. If you don't have trisodium phosphate, continue to step 3.
Open the drain plug underneath the hot tub to remove at least 6 inches of water if you don't want to add trisodium phosphate to lower the calcium hardness. Monitor how much water is removed and replace the drain plug when you have removed 6 inches of water.
Attach the garden hose to the water faucet. Turn on the water and replace the water removed from the spa.
Test the calcium hardness of the water one more time. Assuming that one of the two treatments worked, you should test the other chemical levels. If the level is still high, repeat step 2 or steps 3 and 4.