How do I fix low or high calcium hardness in my pool?

For low hardness, add calcium chloride (hardness increaser) per the label, brush, and retest in 24 hours. For high hardness, you must dilute by draining and refilling with fresh water — no chemical removes calcium. If your fill water is naturally hard, routine partial drains become a seasonal chore. Don’t ignore either: low calcium eats plaster and grout; high calcium clouds water and leaves white crust.