Why Is My Hot Tub Water Green? Your COMPLETE Guide to Fixing Green Hot Tub Water

By Jon Filson

Hydropool Hot Tubs and Swim Spas

Published May 15, 2024

If your hot tub water turns green, there’s no way it isn’t shock. It is!

But don’t be too alarmed. It happens. And it can be fixed. Green hot tub water is generally a sign of imbalance in the water, through lack of sanitization, algae or minerals.

We get this question occasionally – not that often – at our Hydropool retail outlets. It’s not a typical problem but because it’s alarming, we want to make sure we give you good advice here.

Hot tub water that is anything else but transparent is an indication that something is wrong. Actions must be taken to ensure that the water is sanitary before anyone can enjoy a soak.

Typically, temperature, pH levels, and other elements must be on par to ensure that you enjoy a healthy and relaxing soak in your hot tub.

So in this article, we will explain:

  • Why hot tub water can turn green
  • A step-by-step process on what to do if it has turned green

Hopefully, by the end, you’ll know just what to do if it happens to you!



Why Did My Hot Tub Water Turn Green?

Regular Use: Frequent use of your hot tub can cause the water to turn green. In most situations, it is the lack of chlorine in the water that can contribute to its altered coloring. Keep your filters clean and add the appropriate chemicals, cleaners or solutions to your hot tub water. You may also be not using enough sanitizer on a regular basis so consider upping your amount of chlorine or bromine.

Algae: The presence of photosynthetic organisms, such as algae in your water can also change the color of your water.  If algae is the cause, it is typically accompanied by slime and a dark green appearance. This occurrence is usually rare as hot tubs are covered when not in use. However, they can present themselves through improper filtration, lack of sanitizer in the water, and other causes. Figuring out the cause is crucial to ensuring it doesn’t happen again.

To get rid of algae, draining and refilling the hot tub is the best solution. However, before refilling, filters must be cleaned, and the interior of the hot tub must be wiped down to remove the remaining algae. It is important to use a special cleaning product that cleans out the internal hoses in the plumbing as well.

If done correctly, clear water should be the result.

Another action that can be performed is adding more chlorine, sanitizer or other cleaning solutions to your hot tub water. However, balance is key and adding additional solutions can affect this requirement.

Presence of Minerals: Aside from algae, the presence of minerals in the water can cause the water to turn green. This change in color is not accompanied by slime but just the alteration in color.  The introduction of minerals such as iron, manganese or copper, can be the result of the green appearance of your hot tub water.

Copper can be introduced into the water from copper pipes or heat exchangers and natural well water.   It is also possible for central water to be the carrier of these minerals. Additionally, the corrosion of pool equipment or pipes can also play a role in the presence of these minerals in your hot tub water.

Manganese offers discoloration as well, but it is not usually green. A black, brown or purple hue is an indication that this mineral is in your hot tub water.

If you have these elements naturally in your water, you will need to ensure your weekly maintenance ritual addresses them. To solve the presence of any metals, cleaning your filter, or performing the action of shocking is also a way to ride your hot tub of these elements.

If those steps are insufficient in solving the problem on an ongoing basis, head to your local retailer for advice on your specific situation and get your water tested there.

What Steps Can I Take Once My Water Has Turned Green?

If you're dealing with a green water issue in your hot tub, it’s a clear sign that you need to rebalance the chemicals in the water.

Here's a step-by-step guide on how to restore the chemical balance in your hot tub:

Test the Water

Begin by testing your hot tub water using test strips or a liquid test kit. You'll want to measure the pH, total alkalinity, chlorine (or bromine) levels, and the presence of any metals such as copper or iron. The ideal pH level should be between 7.4 and 7.6, and total alkalinity should be between 100 and 150 parts per million (ppm).

Your local retailer can provide you with a more accurate test that goes beyond what test strips can do. If you’re not getting results, or if you want to get it right the first time, head to your local dealer.

Adjust pH and Total Alkalinity

Adjust the pH and total alkalinity levels if they are not within the ideal range:

  • If pH is too high, use a pH decreaser.
  • If pH is too low, use a pH increaser.

To adjust alkalinity, use an alkalinity increaser if it's low, or a pH decreaser if it's high, because lowering pH will also bring down the alkalinity

Shock the Hot Tub

After adjusting the pH and total alkalinity, it's time to shock the water. Shocking involves adding a large dose of chlorine (or non-chlorine shock) to the water to break down organic matter and kill algae. Follow the container instructions for the correct amount of shock based on your hot tub's water volume.

Run the Filtration System

Activate the hot tub's filtration system and let it run continuously for at least 24 hours (on a Hydropool hot tub, this will run automatically, as it is always on). This will help circulate the shock and ensure the chemicals are well-distributed throughout the tub.

Clean or Replace the Filter

While the shock is doing its job, it's a good time to clean the hot tub filter or replace it if it's worn out. A dirty filter can harbor algae spores and other contaminants, so it’s crucial to maintain it properly. It may well have been the cause of the original problem.

Re-test and Rebalance if Necessary

After the shock treatment and a period of filtration, test the water again. Make any necessary adjustments to the pH, alkalinity, and sanitizer levels. If the water is still green or if algae is persistent, repeat the shocking process.

Brush and Clean

Use a soft-bristle brush to scrub the sides of the hot tub and a vacuum to remove any dead algae or debris that has settled at the bottom or on the seats. If you have a self-cleaning Hydropool hot tub, the floor vacuum in the hot tub will remove any particles on its own.

Add Algaecide (Optional)

In some cases, after the shock treatment, you may want to add an algaecide specifically formulated for hot tubs to help prevent future algae growth.

Monitor and Maintain

Going forward, regularly test and adjust the chemical levels, and maintain the cleanliness of your hot tub and filter to prevent future issues.

Why Does My Hot Tub Water Look Green?

We covered a wide variety of the main reasons why hot tub water can turn green in this article. To ensure that you receive the best experience for your tub, it is crucial that you keep it clean and perform regular maintenance.

Maintaining your hot tub eliminates the potential for bacteria growth, clogged systems, dirty filters, unclear water, and a variety of other unsanitary conditions that can harm the cleanliness of your hot tub.

  • Keep your hot tub covered when not in use.
  • Shock your hot tub and clean its filters regularly.

These two steps will do the most to ensure that your hot tub is sterile and always prepared to offer a clean and relaxing experience.

We hope this article has helped you with any green water you encounter! If you have more questions, don’t hesitate to reach out to your local retailer.

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