Why You Might See Yellow Flakes In Your Hot Tub

Jennifer Rhodes

By Jennifer Rhodes · Updated

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A common issue many hot tub owners face is the formation of yellow (or sometimes white) flakes. You might think that this indicates some sort of bacterial build-up in the hot tub. However, don't worry: this isn't the case. If you see yellow flakes, there is most likely another reason behind it. Let's explain.

When you see yellow flakes (or sometimes a white powder residue) in your hot tub, it normally indicates that there is calcium build-up. As long as you don't let the problem get out of hand, it is usually easy to rectify with a few simple steps.

However, if you leave it for too long, you may find that you need to replace components in the hot tub, as excessive scale build-up over time can cause permanent damage. This can get rather expensive, so we'll go over how you can fix the problem in just a second.

What are those yellow flakes in your hot tub?

In most cases, if you see yellow flakes in your hot tub, it means that there is some sort of calcium build-up. In rare cases, it could mean that there is a build-up of bacteria in the hot tub, often called biofilm. However, that is normally quite distinguishable. Calcium build-up will be hard flakes, while bacterial build-up will likely be soft, sticky bits and pieces.

We are mainly going to focus on yellow calcium build-up in this article, but if you think you have a biofilm problem instead, I have another post on how to fix a slimy hot tub.

Calcium build-up occurs because of your water. Water (especially in hard water areas or those with well water) is naturally high in minerals, and these minerals enter your hot tub when you fill it.

For the most part, you should never see the calcium in your hot tub, even if the water that you have used to fill the tub is naturally high in minerals. You will normally only start to notice flakes if the pH levels in the hot tub are allowed to get too high, because high pH contributes to calcium scaling.

If you're struggling with regular maintenance, I have a free printable hot tub maintenance schedule which you can download to remind you of exactly what to do.

This is why most people will often see the calcium build-up only after they haven't used the hot tub for a while, or haven't been keeping on top of maintenance. It isn't really something you will get if you are properly balancing the water in the tub.

How do you remove yellow flakes from your hot tub?

There are products on the market designed to remove calcium deposits from your tub. However, you shouldn't normally need to purchase them. Most calcium build-up can be removed using a few household items. Here's how to do it in a few simple steps.

1. Fish the biggest calcium flakes out with a skimmer

Your first job is to fish all of those calcium flakes out. This won't be the only calcium in the water, but you will be making your life a little bit easier for the later steps here. You can use a standard pool net for this. You should be able to lift the worst of the flakes out this way.

Hand Skimmer
Hand Skimmer
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2. Drain & scrub the walls of the hot tub

Once you have fished out the worst of the calcium flakes, it is time to drain your hot tub. While your hot tub is draining, you will want to make up your cleaning solution. As I mentioned, there are products on the market that can do the job for you, but you may as well make your own solution:

  1. Mix 1-part vinegar to 1-part water in a spray bottle.
  2. When the hot tub has been fully drained, spray the solution on any remaining visible calcium deposits. You should let it sit for about 5-10 minutes. This will allow the vinegar to start to break down the calcium deposits.
  3. After 10 minutes, start scrubbing away. Use a soft nylon brush for this. Note that most of the build-up is going to be around the hot tub jets, so spend some extra time there.

3. Check and clean/replace the filters

If there are a lot of calcium flakes in the hot tub, then check the hot tub filters. They may be clogged too. While you may be able to get rid of the calcium with a deep clean or soak them in a similar vinegar solution, it may be easier to replace them if the calcium build-up is serious.

4. Refill the tub and maintain pH levels

Once the worst of the calcium deposits have been removed, rinse and wipe everything down. Then refill the hot tub.

Get a hose attachment that will filter the water while you are filling your tub. This will reduce the mineral content, and help to minimize any future chance of calcium build-up.

When it is refilled, go through your normal process to ensure that the water is properly balanced:

  • Let your hot tub heat up to a temperature of 100°F (don’t skip this step—chemicals may not work properly if added to cooler water)
  • Add metal free to remove metals from the water which can stain equipment. Circulate for 30 minutes.
  • Add calcium chloride to raise your water’s calcium hardness to 150-250 ppm. You can check your local municipal water supply to find out what the natural hardness of the water is in your area to get an idea of how much you'll need to add. Circulate for 20 minutes.
  • Add sodium bicarbonate to raise the water’s total alkalinity (TA) until it’s within the range of 100-120 ppm. Circulate for 30 minutes.
  • Test the pH, and then add either pH up (alkaline) or pH down (acid) until it’s within the range of 7.2-7.8. Circulate for 30 minutes.
  • Add your sanitizer up to the appropriate levels. You’re aiming for 1-4 ppm for chlorine, and 2-6 ppm for bromine.
  • Shock your spa, and then wait for the sanitizer reading to drop to a safe level. Once it measures in the above ranges, your spa is ready to use!

How do you stop calcium build-up in your hot tub?

Aside from using a hose attachment to fill your spa, the only real way to prevent calcium build-up in your hot tub is to stay on top of your maintenance. Some calcium is always going to be present in the water anyway, so your job is to keep the water balanced (especially pH) so the calcium cannot form scale.

Always ensure that the pH level of your hot tub remains between 7.2 and 7.8. If the pH level goes above 7.8, then there is a strong chance that calcium will start to gather.

If you do notice any calcium flakes or build-up, then make sure you get rid of it right away. You can use the method we mentioned in the previous section for this.

If you live in an area with especially hard water (and your calcium hardness measures above 250 ppm), you can try a scale control product which should help to keep the problem at bay:

Leisure Time 30210A Defender Spa and Hot Tub Stain and Scale Cleaner, 32 fl oz
Leisure Time 30210A Defender Spa and Hot Tub Stain and Scale Cleaner, 32 fl oz
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Summing up

If you see yellow flakes in your hot tub, then it is most likely to be calcium build-up. While this can be a serious problem if it is allowed to get out of control, it is usually something that can be fixed rather easily.

A good scrub of the hot tub will do the trick. To prevent the yellow flakes returning, you must ensure that you maintain proper water balance (in particular pH levels) in your hot tub in future.

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