Dilution is the only reliable fix for high pool hardness.

You’ll need to drain and refill part of the pool.

High calcium hardness almost always comes from your fill water. If you live in an area with hard water, every time you top off the pool you’re adding more calcium. Other common causes: using calcium hypochlorite shock (look for “cal hypo” on the label) or letting the pool evaporate without adding fresh water, which concentrates the minerals.

There’s no chemical that removes calcium. Sequestrants (like stain treatments) bind calcium so it doesn’t scale, but they don’t lower the number. The only real fix is dilution: drain some water, refill with softer water. Test your tap water first. If it’s high, consider trucking in softened water or buying a portable RO filter.

Don’t bother with “hardness reducers” sold at pool stores. They’re mostly fluff and can mess with your chemistry. Drain and refill is faster, cheaper, and proven.