Green Water in Your Hot Tub – How to Fix it the Easy Way

Michael Keenan


Hot Tub Troubleshooting

Are you looking forward to a relaxing spa day only to find your hot tub filled with green water? Your hot tub water is now green and no, that isn’t normal!

The bad news? Your hot tub has algae. The good news? It’s completely treatable and though labor intensive, completely worth it. The best news? You can easily prevent this with a few smart precautions.

There are several reasons why your hot tub can turn green such as inadequate sanitization or over-sanitization and leaving the hot tub uncovered when not in use.

It is easy enough to get rid of green water in your hot tub when you know how. Read on to know how to solve your hot-water-tub woes!

how to fix green water in your hot tub

Quick Answer:

Having green water in your hot tub is totally treatable! It could be caused by inadequate sanitization, algae spreading, a defective filtration system, or leaving the tub uncovered. Preventing algal blooms is key to keeping your hot tub clean and clear.

Cover it when not in use, regularly check and replace filters if needed, and add sanitizer according to the volume of the tub. Cleaning and shocking the water is also important for getting rid of any unwanted algae growth.

But Why Is My Tub Water Green?

Why is your tub green instead of blue, you wonder? A range of reasons could have contributed to your spa’s now-green nature, such as:

  • Inadequate sanitization or over-sanitization, or irregular sanitization.
  • Algae moving homes from an algae-infested pool or water body that you probably visited earlier to your spa; your swimsuit or any accessory that you used in said pool will serve as the mode of transport for said algae!
  • Defective filtration system.
  • Insufficient cleaning and replacement of the hot tub’s filtration system.
  • Leaving the hot tub uncovered when not in use; an outdoor spa is especially conducive to green algae growth, thanks to the added sunlight factor (this is, by far, the most common reason for green hot-tub water).

Why is it important to know why your hot tub water is green?

Well, because prevention is better than cure and knowledge of what causes something leads to prevention. Hot tubs can suffer from a range of problems – here at Outdoor Care Guide we cover the most common ones and how to fix them:

Now that you know why your spa could turn green, look to these steps to prevent algal bloom growth, as well as the following.

green algae in hot tub

Getting Rid of Algae in Your Hot Tub

As I mentioned earlier, getting rid of algae in your tub can be a little back breaking and sweat inducing, but hey, no pain, no gain! Unfortunately, there are no shortcuts to success, especially with a green tub in the picture, so set aside a Sunday and do the following!

Spa Deep Cleaning

Though a spa should generally give you a good deep cleaning, sometimes, you may have to give your spa a good deep cleaning. To do this, drain the hot tub and clean it thoroughly. Get rid of every bit of water in the tub and scrub down the surfaces to ensure that the algae has completely disappeared from all parts of the tub.

Clean and / or Replace the Filter

Unfortunately, just rinsing your hot tub and the filter in clean water won’t get rid of your algae woes – you’ll need to thoroughly clean the filter by applying a filter cleaner. You can even soak the filter overnight in a chemical rinse to be doubly sure that the algae is gone.

If the filter is worn out (or even an overnight chemical soak doesn’t do the trick for you), replace it.

Scrub That Tub!

To completely and thoroughly get rid of the algae, you’ll need to scrub down your tub. You could use diluted bleach, diluted cleaning vinegar, or even any other household cleaning product for this.

If you want to get the job done properly, use a cleaning agent made specifically for hot-tub cleaning, such as this one – Oh Yuk Healthy Hot Tub Cleaner.

Refill Your Tub

Refill your tub, but remember, whether you refill it with well water or city water, using a hose filter is a good idea. This keeps out any contaminants and minerals. The ‘Camco Hose Filter’ comes highly recommended.

Clean the Spa Cover

It isn’t only important to scrub out your tub, but the tub cover as well. Condensation will collect on the cover’s underside, creating a habitat perfect for algal spore growth.

Since you’ll be waiting for the tub to fill up, spend the time cleaning the cover with diluted cleaning vinegar, diluted bleach or a vinyl cleaner, instead of twiddling your thumbs!

Again, you might want to use a cleaner built specifically for hot tub cleaning, like the 303 Products Multi-Surface Cleaner.

303 Marine Multi-Surface Cleaner
Safely Cleans All Water Safe Surfaces, Including All Types of Fabric and Vinyl, Rinses Residue Free, Manufacturer Recommended, 32oz

Shocking the Water

Like a pool, shock your hot tub too. Shocking involves the addition of chlorine or non-chlorine chemicals to the water to prevent any bacteria and algal growth. Give your tub a good shock to keep the algae at bay. The ‘Spa Essentials Dichlor Chlorine’ is a good call.

Spa Essentials Xtra Chlorine Shock (6 lb)
SPARKLY SPA: Restore your spa’s sparkle with this extra-strong shock treatment. REMOVES ODORS: Easily removes unpleasant odors and adds clarity to the water. WORKS WITH: Uses dichlor chlorine that’s compatible with chlorine, brome, and ozone

Testing the Waters

Quite literally, it’s time to test the waters! Once the shock has “worn off”, test the water with a liquid test kit or test strips – the AquaChek Select Spa Test Strips are pretty efficient and get the job done well. With a testing strip, you can test for total chlorine, bromine, free chlorine, pH, alkalinity, cyanuric acid and hardness levels.

See my guide on testing your hot tub water to learn how to do this quickly and accurately.

Balancing the Water

After the chemicals that you’ve added in have had the time to dissolve and disperse, test the water again. If the figures are off, you’ll need to add them again to get the balance right and repeat this entire step again or as many times as required, till the right balance is achieved.

Yellow Water in Your Hot Tub?

Don’t worry if the water has turned yellow – it’s not an additional problem to deal with, but it’s likely a part of the same problem! Yellow water means that you still have an algae problem, but of a different kind – your tub has been afflicted with mustard algae, quite rare in areas with a cold climate.

Unfortunately, getting rid of yellow algae takes even more work than getting rid of green algae. To make it even worse, such algae are even known to be resistant to chlorine.

Don’t give up though. Follow the same cleaning steps listed above and persist!

yellow algae in hot tub

How to Prevent Algae In Your Hot Tub

There are many small but effective things that you can do to prevent algal blooms in your hot tub. Some of these include:

  • Cover your hot tub at all times when it’s not in use, even if it’s an indoor tub.
  • Regularly check the filtration system for damage or defects. This way, you can replace any worn-out filters in a timely manner.
  • Manage your hot tub water chemistry – keeping it balanced.
  • Change your spa water at set intervals or after heavy use.

If you’ve used your swimsuit or swimming accessories in a pool or tub other than yours, wash them before you get into your pool or tub. This prevents the risk of any algae hitching rides on your clothes and accessories.

Ensure that you add sufficient amounts of sanitizer to your hot tub – base this on the volume of the tub. Additionally, add sanitizer in the regular intervals that you’re supposed to add it in – you can keep a check on this by testing the water regularly.

Consider using some of these alternative hot tub sanitizers to get your water quality just how you like it.

dirty spa

Common Questions:

What are the potential causes of green water in a hot tub?

Potential causes of green water in a hot tub include high levels of bacteria, algae, and minerals from the fill water.

How often should you clean and maintain your hot tub to prevent green water?

Hot tubs should be cleaned regularly to prevent green water; maintenance should include testing, cleaning and changing the filter every 3-4 months.

What products can be used to treat green water in a hot tub?

Chemical treatments such as chlorine or bromine shock can help reduce bacteria and algae that cause green water in a hot tub.

What safety precautions should be taken when treating green water in a hot tub?

Safety precautions should include wearing protective clothing such as goggles and gloves. Ensure there is proper ventilation while handling chemicals, checking chemical levels with test strips after treatment, and avoiding contact with skin when adding chemicals to the spa.

The Bottom Line

If your hot tub water has turned a greenish hue, it’s probably due to algae. To get rid of the algae from your hot tub, you’ll need to thoroughly clean it by scrubbing down the surfaces with a cleaning agent made specifically for hot-tub cleaning. You should then shock the water with chlorine or non-chlorine chemicals.

Algae in hot tubs can be incredibly hardy so even after taking all necessary steps it may take two or three tries to completely remove them from your spa.

With a few preventative measures such as covering your hot tub when not in use, regular maintenance of the filter system, and adding sanitizer to the water regularly, you can avoid this issue all together. With regular maintenance and prevention strategies, you can keep your hot tub clean and ready to enjoy!

Last update on 2024-06-17 / Affiliate links / Images from Amazon Product Advertising API

michael keenan author

Author - Michael Keenan

I'm Michael Keenan the owner and creator of the Outdoor Care Guide. I'm a trained horticulturist with over 30 years of experience in pool care, plant care, and landscape care! Seemed like a good idea to share - I think I can make your life easier and save you some time and money!