Total Hardness

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Ideal Total Hardness Range for Hot Tub: 150-250

Testing Total (Calcium) Hardness:

To check your hot tub’s total hardness, you can either bring a water sample to your local dealer for professional testing or use a high-quality home test kit for quick results.

What is Total Hardness?

Total hardness measures how “hard” or “soft” your hot tub water is — in other words, how much calcium and magnesium it contains.

Keeping total hardness in balance is just as important as managing pH and Total Alkalinity. If the levels are off, your water can become corrosive (damaging surfaces and equipment) or scaling (leaving white deposits).

Before adjusting calcium hardness, always balance your water in this order:

  1. Total Alkalinity
  2. pH
  3. Total Hardness

The ideal total hardness level for a hot tub is 150–250 ppm (parts per million). To check if your water is properly balanced, use our Langelier Saturation Index (LSI) calculator.

Low Total Hardness

When hot tub water becomes too soft (i.e. its total hardness drops below 150 ppm) it becomes corrosive. If you don’t manually add calcium or magnesium back into the hot tub, the water will begin to take what it needs from any part of your hot tub and equipment that contains stone, concrete, metal, grout, etc. Problems often associated with low calcium hardness include:

  • Eroding of tile grouting and delaminating of plaster surfaces
  • Etching or pitting of hot tub decks/stairs or stone and concrete surfaces surrounding your hot tub. Corrosion of metal parts (i.e. pipes, heating elements, pump seals, internal parts on gas fire heaters, etc.)
  • Pitting of hot tub flooring and walls

Once damage from soft water occurs, there’s no way to undo it. It’s essential not to let your hot tub’s total hardness drop too far below 150 ppm.

How to Raise Total Hardness in Your Hot Tub

If your hot tub’s total hardness level drops below the recommended 150 ppm the easiest and most common way to raise calcium hardness is by adding a calcium hardness increaser such as calcium chloride to your hot tub.

High Total Hardness

Similarly to when the hot tub’s pH level is too high, when a hot tub’s total hardness level is too high it becomes basic and over saturated with dissolved particles including calcium. Over time, the water will become cloudy and the excess amount of dissolved particles in the hot tub will cause the water to scale in and around your equipment, possibly clogging and blocking the flow of water in and out of the hot tub, which can damage your hot tub equipment.

How to Lower Total Hardness in Your Hot Tub

There is really only one way to lower your hot tub’s high total hardness level and that is to partially or completely drain your hot tub water and replace it with fresh water.

FROG Fresh Mineral Water∞ is softer because minerals condition the water for softness so it’s easier on you and your pool or hot tub with no faded suits or smelly odors.

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