Save Time And Money With Our FREE Hot Tub Cheat Sheet
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.

How to Remove and Prevent Hot Tub Stains

Matt Giovanisci, Founder and CEO of Swim University By Matt Giovanisci | September 20, 2020

You’ve gotta be kidding. You clean your hot tub, you put sanitizer in it, and it still developed stains in the shell. How did that happen?! Hey, don’t beat yourself up. We’ve been there. It may not really be your fault. Your spa can develop stains even if you’re doing everything right. You may just need to make a few adjustments, that’s all.

Prevention is, of course, key. But before you can work on that, you need to know how to remove hot tub stains. Start with a clean slate (or in this case, shell), and it’ll be a lot easier to keep them from coming back.

What Causes Hot Tub Stains?

Obviously, if you don’t clean your spa on a regular basis, it’s going to develop stains, just like anything else would if you left it dirty all the time. But what about when you have been cleaning it, and stains still show up? What’s going on?

This is because hot tub stains can be caused by a few factors aside from dirt:

Calcium Buildup

If you live in an area with hard water, it’s only a matter of time before you start seeing the telltale signs of hot tub scale in the shell.

The calcium and magnesium in the water—high levels of which are what make it hard—will slowly begin to deposit scale on hard surfaces. And not just the shell, but the fixtures too.


Your water source may contain high levels of metals such as iron and copper. This is especially true if you get your water from a well. Over time, the metals will react with the chlorine in the water, and oxidize, or rust.

When you see greenish-brownish-red stains on the shell, there’s probably a lot of iron in the water. If the stains are blueish-greenish-black, that’s an indication of high copper content.

Scum Buildup

The same way body oils and bathing products can leave a ring around your bathtub, those same contaminants can be released into the water when you go for a soak.

Then, those contaminants are deposited onto the shell, leaving an ugly ring of hot tub scum. Left long enough, it can stain the fiberglass, no matter how much you scrub.

Luckily, none of these issues is impossible to remedy.

How to Remove Hot Tub Stains

It’s going to come down to good, old-fashioned elbow grease to get rid of hot tub stains. But the substances you use may differ depending on the type of stain you’re dealing with.

Test the Water

To know what type of cleaner you’ll need, it’s crucial to test the hot tub water first. If you suspect the problem may be with high metal levels (if you use well water, for example), make sure the testing strips or kit you use measures for at least iron and copper.

Here’s what you need:

Metals Test Strips for Pools & Hot Tubs

This water testing kit offers a convenient way to monitor water quality without the need for reagents. It tests for iron and copper with a range of 0 to 5 ppm and 0 to 3 ppm.

Buy Now On Amazon
If you click this link and make a purchase, we earn a commission at no additional cost to you.

All that’s left is to get to work.

  1. Shock the hot tub to kill bacteria.
  2. Clean the plumbing with the hot tub line flush product.
  3. Turn off the hot tub.
  4. Turn off the hot tub breaker to ensure it’s not receiving any electricity.
  5. Drain and clean your hot tub, using the cleaning product that corresponds to the type of stains you’re removing, and scrubbing the stains thoroughly with the nylon sponges.
  6. Clean the hot tub filter; replace it, if necessary.
  7. Rinse the shell thoroughly; cleaner residue can cause a foaming problem, and you’ll have to start over.
  8. Inspect the stained areas; if any stains remain, scrub them again, and rinse again.
  9. Dry the fixtures and other areas around the hot tub that won’t be filled with water.
  10. Refill the hot tub; if you have hard water or high metal content, use a hose filter.
  11. Balance the water.
  12. Test the water; balance again if necessary.
  13. Get back to soaking!

To keep from having to go through this process again, take a few steps to prevent stains from forming again.

Our Top Pick
Hot Tub Detox: Line Flush & Plumbing Purge

Don't let your hot tub fill with hard-to-remove gunk. Clear out the gunk and keep your hot tub water fresh. It removes gunk in your pipes caused by lotions, sunscreens, cosmetics, etc.

Buy Now From Swim University
The Hot Tub Care Video Course
Tired of wasting time, money, and chemicals trying to keep your hot tub clean?

Cut the confusion with our easy-to-use video course. Save $1,000's on hot tub care and keep your water clean and clear for good!

Learn More

How to Keep Hot Tub Stains From Returning

So how do you stop stains from forming in the first place? I can sum it up in two words: water chemistry. That’s right. If you keep the hot tub water balanced, stains will have a difficult time forming. The most important tactic is to keep the hot tub pH balanced.

Now, this doesn’t mean that you won’t have to drain your hot tub periodically and give the shell a good cleaning. Nothing will ever free you from that. But it does mean stains will be a lot less likely to come back. To make that even more likely, you can take a few extra steps, depending on your water.

Hard Water

Add a calcium hardness reducer or a scale prevention chemical to the water. Follow the manufacturer’s instructions to ensure you add the right amount.

Tip: You’ll need to know how many gallons of water are in your hot tub. You need to know this to add any chemicals and keep the water balanced, so it’s important to determine this, and keep the information handy for proper maintenance.

High Metal Content

To keep metals from oxidizing in your spa, use a metal sequestrant. This chemical doesn’t remove metals. Instead, it causes the metal molecules to clump together so they can be caught in the hot tub filter. Follow the manufacturer’s instructions for use.

Hot Tub Metal Remover
$9.19 ($0.57 / Fl Oz)

Quickly remove metals like iron and copper from your hot tub water.

Buy Now on Amazon
If you click this link and make a purchase, we earn a commission at no additional cost to you.
05/20/2024 10:03 am GMT


You can’t possibly keep body oils and toiletry residue out of hot tub water. You can try to keep it from building up on the shell. Special floating sponges are made precisely for this purpose, but if you don’t have any on hand, two or three tennis balls will do.

Stains Don’t Have to Be Pains

Hey, no one wants to take a soak in a dirty hot tub, much less a stained one. Knowing how to remove hot tub stains is just as important as knowing how to prevent them because no matter how hard you try, you may still end up with a stain or two now and then.

Just know, they don’t have to be permanent. With the right materials and some perseverance, you can keep your hot tub looking like new for many years to come.

Happy Soaking!

Need More Hot Tub Maintenance Help?

Matt Giovanisci, Founder and CEO of Swim University
Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1993. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
Save Time And Money With Our FREE Hot Tub Cheat Sheet
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.

Featured Hot Tub Products