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What to Do If Your Hot Tub Water Is Green

By Matt Giovanisci | Updated: March 13, 2019

When you first saw that green tinge to the water in your spa, you thought it was a trick of the light. A reflection. Nothing to worry about. But now, you can’t deny there’s a problem—your hot tub water is green. And not just a little green. But green.

The bad news is, your spa has algae. The good news is, though it’ll be a little labor-intensive, it is treatable, so you can get your hot tub back to normal. It’s also preventable with just a few simple precautions.

Why is Your Hot Tub Water Green?

In other words, how did your spa become infected with algae? One or more factors can create an algae-hospitable environment:

Knowing why it’s happening is important because these will be the first steps you take to prevent algae blooms in the future.

How to Prevent Hot Tub Algae

You thought you were doing everything right, but you still woke up to green hot tub water. You may have been laying out the welcome mat without even realizing it. Pick that up, and put out a no trespassing sign instead.

Those few simple tactics will help keep algae from forming again. But first, you need to address the algae already in the hot tub.

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How to Get Rid of Hot Tub Algae

You’ll need to set aside some time to do this so you can do it properly. Once you’ve noticed your hot tub water is green, you can’t take any shortcuts in clearing it up.

1. Deep Clean the Spa

The first step is to drain and clean the hot tub. You have to get rid of the water that has algae in it, and then clean every surface to make sure every bit of algae is gone.

2. Clean or Replace the Filter

With an algae problem, just rinsing the filter with clean water won’t be enough. You’ll need to apply a filter cleaner. You may even want to soak it overnight in a chemical rinse to be absolutely sure it’s free of algae.

If that doesn’t make you comfortable enough, or if the filter is just worn out, now’s the time to replace it.

3. Scrub-a-Dub That Tub

Just a wipe-down won’t do. Break out the hot tub cleaner for a total and thorough shell cleaning. Or, if you prefer, you can use diluted bleach, diluted cleaning vinegar, or some other household product to clean your hot tub.

For an algae problem, though, we highly recommend using a cleaner made for hot tubs.

4. Refill the Hot Tub

Regardless of whether you use city water, or you get your water from a well, we highly recommend using a hose filter. This will help keep minerals and other contaminants out of your hot tub.

5. Clean the Cover

Because condensation will collect on the underside of the hot tub cover, it’s entirely possible that a few algae spores have set up shop there. While you’re waiting for your hot tub to refill, clean the cover with diluted bleach, diluted cleaning vinegar, or with a vinyl cleaner. Again, when dealing with algae, we recommend using a cleaner specific to the task.

6. Shock the Heck Out of It

One the tub is full, shock the hot tub. Then shock it again so algae won’t even think about coming back.

7. Test the Water

Once the shock has had time to dissipate, test the water either with test strips or a liquid test kit. This will give you a baseline so you’ll know what chemicals to add, and how much.

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8. Balance the Water

Give the chemicals you’ve added a little time to disperse, then test the water again. If everything’s where it should be, great! You’re all done! If not, adjust as necessary, wait a little while, and test again, repeating the process until the water is properly balanced.

But … My Water is Yellow!

What if the problem isn’t that your hot tub water is green, but that it’s yellow? You likely still have an algae problem, just a different type.

Yellow algae, also known as mustard algae, is a rare form of algae found most commonly in areas with a warmer climate.

Yellow algae is tough to get rid of and has even been known to be chlorine resistant. So if you’re looking at yellow water, follow the algae cleaning steps slowly and carefully.

What About an Algae Encore?

After you’ve followed all the steps to get rid of algae, it’s gone. Or is it?! Algae—both green and yellow—is tough stuff, and the truth is, it may take two or even three tries to get rid of it completely, so be prepared for that possibility.

You: 1 Algae: 0

You’re now on your way to winning the war against algae that makes your hot tub water green or yellow. But it’s a never ending battle, and you must be vigilant. It can sneak back into your territory at any moment.

Take the proper precautions, keep your hot tub clean, and keep the water balanced, and you’ll maintain a strong, algae-free front line.

Happy Soaking!

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. 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.
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