A Comprehensive Guide to Managing Calcium Hardness in Your Hot Tub


When it comes to maintaining a hot tub, one often overlooked but critical factor is calcium hardness. This measure is instrumental in hot tub water chemistry, and ignoring it can lead to serious consequences, including component damage, bacteria, skin and eye irritation, and scaling. In this comprehensive guide, we will delve into what calcium hardness is, the impact of low or high levels, and how to effectively balance calcium hardness in your hot tub.

What is Calcium Hardness?

Calcium hardness is the measure of the amount of calcium dissolved in your hot tub water. The hardness of your water largely depends on your location. If you reside in the South of England, you likely have “Hard Water,” characterized by a high calcium content in your water source. Conversely, in regions like Scotland, Wales, or the North of England, you probably have “Soft Water,” which contains minimal calcium.

Determining whether your water is hard or soft can be as simple as visiting your local water supplier’s website. Additionally, the plumbing on your property may have a built-in water softener, which can reduce water hardness.

Why is Balancing Calcium Hardness Important?

Balancing calcium hardness in your hot tub is crucial to prevent the buildup of various issues, depending on whether the calcium level is too high or too low.

High Calcium Hardness:

  1. Scale Build-Up: High calcium levels, combined with imbalanced pH, can lead to scale build-up on hot tub fittings. This can result in white deposits clogging your filters and negatively impact your hot tub’s components’ lifespan and overall performance.
  2. Irritation: Excessive calcium hardness can make it challenging to maintain the right pH levels, leading to eye and skin irritation for hot tub users.
  3. Cloudy Water: Loose scale floating around your hot tub can reduce water clarity, affecting the overall experience.

Low Calcium Hardness:

  1. Corrosion: When calcium levels are too low, the water may become corrosive. This can lead to fittings and hot tub parts corroding as the water seeks to source calcium from the components and metals in your hot tub.
  2. Slimy Water: In some cases, inadequate calcium hardness can result in water that feels slimy to the touch, detracting from the hot tub experience.

It’s worth noting that if your hot tub features a salt system, maintaining proper calcium hardness becomes even more critical. This is because it helps stabilize pH levels and prolong the life of the cell or cartridge responsible for electrolysis. High water hardness can lead to scale formation on the surface of this critical component, significantly reducing its lifespan.

How to Test for Calcium Hardness and Ideal Levels

Testing for calcium hardness in your hot tub is a straightforward process. You can use a test strip, either Aquachek 6-Way Test Strips or Hot Spring 5-way Test Strips. The ideal calcium hardness level for your hot tub should fall within the range of 75-150ppm. However, for hot tubs equipped with salt systems, the target range is slightly lower, ranging from 25ppm to 75ppm.

Managing Calcium Hardness Levels

Lowering Calcium Hardness:

Lowering calcium hardness can be challenging, but it is possible. The best approach is to fill your spa or hot tub with soft water. If you have a water softener at home and the tap water measures the correct hardness level, use this water to fill your hot tub. Alternatively, you can employ a portable water softener, which can be easily recharged in under 15 minutes and will last for years.

If your hot tub is already filled with hard water, you can remove calcium using a product like the “Vanishing Act Calcium Remover.” This product, designed for various hot tub brands, effectively reduces calcium levels. Simply run your pump for 24 hours with the Vanishing Act bag covering the suction to allow all the water to pass through it and remove calcium flakes. Dispose of the bag afterward. If the calcium level remains high, use an additional bag.

Increasing Calcium Hardness:

To increase calcium hardness, add a Calcium Hardness Increaser product to your hot tub. Ensure you dose cautiously, as overdoing it can lead to the need for subsequent reduction.


Is Calcium Hardness the Same as pH?

No, calcium hardness and the pH level are distinct measures. Calcium hardness pertains to the amount of calcium in your water, while pH measures the acidity or alkalinity of the water. However, these two factors are interconnected, as high calcium hardness can make pH management challenging. To prevent scale build-up and ensure water balance, it’s essential to maintain both calcium hardness and pH at appropriate levels.

How to Remove Scale Build-Up from Your Hot Tub?

If scale has already formed in the filter of your hot tub due to imbalanced calcium hardness and/or pH levels, you can address it using an anti-scale product like “Happy No Scale” or “AquaSparkle ScaleAway.” After applying the product, remember to clean your filters a day or so later for optimal results.

In conclusion, understanding and managing calcium hardness is a fundamental aspect of hot tub maintenance. By maintaining the correct calcium hardness levels, you can ensure a more enjoyable and long-lasting hot tub experience. Whether you need to increase or decrease calcium hardness, there are effective solutions available to keep your hot tub water in perfect balance.


  • Jason

    Jason is an experienced writer, having contributed to many popular websites over the years. He currently writes for Big Hot Tub, a blog about everything hot tubs. When he's not writing or working on his blog, Jason enjoys spending time with his wife and two young children.