Total Hardness

Hot Tub Header Mask

Ideal Total Hardness Range: 150-250 ppm

Testing Calcium Hardness:

Also known as “Calcium Hardness,” and “Water Hardness.” We recommend taking a sample of your swim spa water to a dealer test station or using an advanced test kit.

What is Total Hardness?

Total Hardness is the measure of how hard or soft your swim spa water is and measures the amount of dissolved calcium and magnesium in it.

Just like pH and Total Alkalinity, it’s important to keep the Total Hardness balanced to prevent your swim spa water from becoming corrosive or scaling.

However, before you begin to balance your swim spa’s Total Hardness level, always balance water to match ideal ranges in this order:

  1. Total Alkalinity: 80 – 120 ppm
  2. pH: 7.2 – 7.6
  3. Total Hardness: 150 – 250 ppm

For more information to determine if your swim spa is properly balanced use our Langelier Saturation Index (LSI) calculator.


Low Total Hardness

When swim spa 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 swim spa, the water will begin to take what it needs from any part of your swim spa and equipment that contains stone, concrete, metal, grout, etc.

Problems often associated with low Total Hardness include:

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

Once damage from soft water occurs, there’s no way to undo it. It’s imperative not to let your swim spa’s Total Hardness dip too far below 150 ppm.

How to Raise Total Hardness in Your Swim Spa

If your swim spa’s Total Hardness level drops below the recommended 150 ppm the easiest and most common way to raise Total Hardness is by adding a Total Hardness increaser such as calcium chloride to your swim spa.

High Total Hardness

There is really only one way to lower your swim spa’s high Total Hardness level: partially or completely drain your swim spa water and replace it with fresh water.

Once filled with fresh water, test it for Total Hardness; a simple hose filter from your local dealer can solve this.

Then, test it for metals; if it test high for metals, use a metal out product.

Check out the Swim Spa Water Balance Guide for help. Or download the FREE FROG Water Care App at the App store or on Google – you’ll get help 24/7!

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