Calcium Scale in a Hot tub

Scale is a mineral based build up that happens in a hot tub when the water is out of balance. There are multiple factors that determine if your tub will develop hot tub scale. This mainly affects hot tub owners that live out of town and have to use well water to fill their hot tubs or if phosphates are present in your source water. 

Types of Hot Tub Scale

There are 4 types of scale that happen in spa water– calcium phosphate, calcium carbonate, calcium sulfate and barium sulfate. There are various methods of prevention and treatment for each type of scale. The best thing to prevent hot tub scale is to find a hot tub professional you trust that understands the different scale types, how they form, why they form and together you can work on a plan of attack for you and your unique water conditions.

Where Hot Tub Scale Comes From

Calcium hardness from well water contributes to scale because of the high amounts of calcium present in the water. First factor to look at is the pH in a hot tub. Ideally a hot tub’s pH should be between 7.4-7.6. A hot tub generally has a high temperature which mixed with a high pH level can cause calcium to build up on the surface of a person’s hot tub. Alkalinity can also affect scale build up in a hot tub. Totally alkalinity is a buffer for pH. It will help control a pH level that is in a hot tub. Generally if alkalinity is high in a hot tub, the pH will be high. If alkalinity is low in a hot tub, the pH will be low in a hot tub. There are exceptions of course where the alkalinity and pH may be on opposite ends of the spectrum.

Scale in pipe

Other Sources of Scale

Another cause of scaling or calcium deposits in your hot tub is PHOSPHATES. These little guys cause demands on your sanitizer, are food for algae, and can bond with calcium ions to create scale. The best way to prevent this type of scale is to remove phosphates at a fresh fill and when you are topping up your water. You should also avoid adding spa care products that contain phosphates – just like high fructose corn syrup, phosphates are everywhere!

Why should I care about hot tub scale?

Scale build up in hot tubs is an issue because it can start to clog plumbing and build up on metal surfaces. This is also a clear indication that there is a water imbalance in the hot tub. When plumbing starts to become clogged, this prevents good circulation of water through the spa which can be hard on equipment. Scale will also start to build up on the acrylic surfaces of the hot tub. This leaves an uncomfortable feeling to sit on for hot tub users.

What should I do if I see scale in my hot tub?

In order to remove scale from surfaces, hot tub owner can take a cloth to remove the grainy particles. Work with your local spa water specialist if the scale is ‘stuck’ and they can analyze your water and give you treatment recommendations.

In order to prevent the scale from coming back, hot tub owners must balance their water to unsure they are in the recommended ranges for pH, alkalinity and calcium hardness. For people that have well water it is hard to bring down the calcium level in hot tubs because their source water generally has high calcium. The recommendation is usually to fill half of their hot tub with softened water and half with hard well water. This generally brings the calcium levels into the range that is recommended for hot tubs. Don’t forget that you should also be applying a stain and scale preventer. This is a chemical that prevents that formation of scale in hot tub water. In order to remove scale build-up from plumbing, use a hot tub flush product when you drain and refill their hot tubs. This helps remove scale from pipping and heater surfaces in order to prevent the plumbing from getting clogged.

The take away about scale in a hot tub is that it takes time to develop and it takes time to get rid of it. Like most things in life, the best prescription is prevention.


  1. John Duerwaechter


    Just want to be able to keep PH at safe level. Also should I add chemicals 1 at a time? Thank you, John

    • Kathi B


      Hi John: ph at an ideal level is 7.4-7.6. Water testing on your own is excellent and partnering with a pool and hot tub professional is also a good. Many products can be added together but always follow the package directions.



    We recently had a problem with a brownish colored sticky buildup around the water line of our hot tub. Kept draining & cleaning it, but it always came back. Hot tub manufacturing company said it was a Soy problem that hot tubs sometimes get. Mind you, we had a hot tub for over 25 years & never had thus problem. We moved down south, git this hot tub & within a year we developed thus gooey, sticky mess. The company flushed everything out with special chemicals & all was good for about 6 months. We are now having the same problem so I am assuming it is the water. I am buying a filter for my hose & will drain & refill. Hopefully thus will solve our problem. My water tested says everything is balanced. What in the world could this gooey, sticky residue be?????

    • Kathi B


      In my experience what you have sounds like it is organic. A biofilm probably. What kind of regular chemical care routine do you follow? Specifically do you use bromine or chlorine? How often do you shock and what do you shock with?

  3. Jenn


    Hi, my water is quite hard. I was told to use weekly descaler which I do. Any time I even get close to the proper ph level my water becomes cloudy- what do I do? It clears up if Iower it. Will the cloudiness clear up eventually and the ph will stay in normal range? I hate having a cloudy hot tub but my skin is bothered by low ph

    • Kathi B


      Hi Jenn: can you let me know a little more….what brand of scale prevention and how much how often? All ‘recipes’ are a little different and some work better than others. Also, what pH and what total alkalinity are your targets? Some test strips and some hot tub dealers have different ranges so i just want to give you the right advice the first time :).

  4. Deborah robeson


    My tub has a salt like film on my jets n tub I bought some scale n stain remover today but it dont seem to be working pls help . I tried scrubbing the jets but it won’t come loose. Ty

    • Kathi B


      that is a great question! scale takes time to deposit and also takes time and good water balance to remove – it is to stubborn to try and rub/scrape off – the chemistry is stronger than elbow grease. Can you let me know the last date of your water test here so i can look up the results and give you some more specific advice?

      besides Spa Guard Stain and Scale for prevention, SpaGuard Lo n Slo will be vital to get your ph in the 7.4-7.6 range.

  5. Kemberly Martin


    Hi I have a sticky orangish substance in my hot tub. I have drained it, cleaned filter and refilled but it has returned. The ph was low and I used ph up and sanitizer. I also use a bromine floater. Any ideas?

  6. Carl wilkes



    I keep getting white flakes in the tub. My ph is marginally lower than I would like and I have to keep adding to it. Alkalinity and chlorine are well managed. Any ideas ?

    • Aqua Tech


      Hi Carl,
      I would come in to get your water tested! Just so we can chemically see what’s going on in there and give the best advice. 🙂 Photos also always help when you bring in a water test, so if you can get a photo of the white flakes when you come in, that would be awesome!

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