What is total hardness?

Most local water supplies contain minerals like calcium carbonate, magnesium, iron and copper. Total hardness measures the total concentration of these dissolved minerals, especially calcium.

Why test it?

Measuring total hardness helps you better understand other tests, such as total alkalinity and pH balance. When the total hardness is out of range, this informs which water balancing products and/or cleaning products you may need to use. Ultimately, it helps to maintain water clarity and avoid eye, nose and skin irritation, plus it helps to protect internal hot tub components.

How is it measured?

Total hardness is measured in parts-per-million (ppm) using a test strip. The target range is between 150 and 250 parts-per-million (ppm).

  • Why is “low” total hardness bad? Total hardness below 150 ppm is generally an indication of low calcium, which goes hand in hand with lower pH (higher acidity). Low pH can irritate your eyes, nose and skin, reduce the effectiveness of sanitizers, and may corrode internal hot tub components.
  • Why is “high” total hardness bad? Total hardness above 250 ppm is generally an indication of high calcium. When excess calcium accumulates inside plumbing lines and on internal hot tub components, it can reduce their efficiency and shorten their lifespan. High calcium may also reduce water clarity, increase water spots, increase flaky or sand-like deposits, and leave an ugly ring of white buildup (called “scaling”) on your hot tub’s acrylic surfaces.

Need help?

Use two clean water bottles to collect these samples: 1) a water-supply sample from your water source, and 2) a mid-depth sample of your hot tub water. Seal each sample tightly, label each one, and bring them to your nearest Marquis Dealer for testing.

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What is total alkalinity?

What is pH balance?

Testing sanitizer levels


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