How to Lower (or Raise) Water Hardness in a Hot Tub

How to Lower (or Raise) Water Hardness in a Hot Tub

When it comes to hot tub maintenance, understanding how to regulate water hardness is paramount. But why should we care about the calcium content in our hot tubs, and how can we manage it effectively? 

Understanding Calcium in Hot Tubs 

All water contains calcium. Calcium is universally present in rivers, oceans, or your home faucets. Dissolved minerals like calcium and magnesium contribute to "water hardness." The water hardness level can vary based on your location and water source. Testing kits are available for purchase if you are still determining your water's hardness. 

Water Hardness vs. Calcium Hardness: A Clarification 

These two terms refer to the same thing. But to make it slightly more complicated, let's introduce a third term: total hardness. This measures both the calcium and magnesium present in the water. While you can get into the details of each mineral's content, knowing the total hardness suffices for most hot tub maintenance purposes. 

Why Manage Water Hardness? 

Too much calcium in your hot tub can lead to scaling. This can appear on visible parts, like jets, and in less noticeable areas, such as pipes or pumps. When calcium buildup impedes the water flow or affects the pump's impeller, it can lead to expensive repairs. High calcium levels can also upset the pH and alkalinity balance in the hot tub, resulting in a cloudy appearance or white flakes. 

On the other hand, too little calcium can corrode your equipment and cause the foam to appear. 

The sweet spot? Keep calcium levels between 175 parts per million (ppm) and 250 ppm. 

Testing Calcium Levels 

  • Test Strips: A simple method that provides instant results. Ensure the strips measure total hardness. 
  • Liquid Test Kits: Slightly more accurate than strips but require more effort. 
  • Professional Testing: Consider getting a professional test from a hot tub supply store twice a year. 

We advise checking water hardness at least weekly or more if your hot tub sees frequent use. 

Lowering Water Hardness 

If your calcium level is slightly above 250 ppm: 

  • Drain a portion of the hot tub water. 
  • Refill with fresh water. 
  • Add a scale control product as directed. 

If it's considerably above the limit: 

  • Empty and clean the hot tub. 
  • Refill with water through a hose filter. 
  • Apply a scale control product for balance. 

Raising Water Hardness 

Suppose your spa's water is too soft. In that case, it's time to add calcium chloride, the key ingredient in many calcium hardness increasers designed for hot tubs. Always follow the product's guidelines. 


Understanding and managing calcium hardness ensures a safe and enjoyable hot tub experience. Regular testing and timely interventions prevent issues like scale, foam, or cloudiness. Remember, a balanced hot tub is the key to uninterrupted relaxation.