Calcium Hardness is important to balance in a spa if Perfect Balance is not being used. Low hardness can corrode the heater and damage the spa surface, as well as contribute to excessive foaming. High hardness can cause scale build-up and cloudy water. The higher water temperature of a spa makes it more difficult for calcium to stay in solution, so it is recommended that Stain & Scale Control be used weekly to prevent any scale build-up.
If you are using the AccuScan to test hardness, you are actually testing total hardness, which includes magnesium. Normally, the level of magnesium does not contribute much to the total hardness reading. You should not notice significant differences between the Wet Lab test, which measures only calcium hardness, and the increased accuracy of the readings from the AccuScan. In most cases it will not effect the ALEX recommendations.
If a water softener like Optimiser Plus was used when filling the spa, replace the calcium as soon as possible. Softeners eliminate calcium from the water and can cause equipment damage and surface corrosion. Follow label or computer recommendations for amount of Balance Pak 300.