You walk out to your garden, pull the cover off your hot tub, and the water is green. This can be a shocking turn of events and can be genuinely scary. However, you don’t need to worry – while it may look worrying, it is surprisingly easy to fix green hot tub water.

In this guide, we are going to explore the causes of green water in your hot tub, what it means, and how you can fix it. When you’re ready to get started, read on and get started cleaning your hot tub.

How to Treat Green Hot Tub Water

If your hot tub water is green, you will either need to use hot tub shock to kill algae or empty your hot tub and clean it.

What Causes Green Hot Tub Water?

Green water is an unpleasant issue to have to deal with, and there are two main causes of it – Algae and minerals.


The most common cause of green hot tub water is algae in the water, which is itself a symptom of the water not being sanitised regularly enough. However, this isn’t the only issue that can lead to green water.


Minerals, including iron and copper, can also lead to green water. These minerals can get into your hot tub’s water from the pipes or corrosion. If you live in an area with high levels of minerals in the water, this could also cause green water.

The solution to either case is relatively similar, but will require different products and approaches.

How to Determine the Cause

Algae is the most common cause of green pool water, so it is worth attempting to work on this as your first line of treatment. If this doesn’t work, then you can move on to trying out solutions to fix minerals in your water.

The First Step: Treating Algae

The very first thing that you need to do is test your water and determine the sanitizer levels in your hot tub’s water. To do this, you will need to use test strips. For reference, chlorine levels should be 3ppm, while bromine levels should be between 3-5ppm. For more information on testing, we recommend reading our guide to hot tub maintenance.

If the sanitizer levels aren’t high enough, algae will grow in your hot tub. Over time, sanitizer levels will drop, and more should be added at least once per week, one of the key reasons that daily testing is required. While sanitizer levels drop over time, they can also drop dramatically if you have used your hot tub a lot in a short time.

Sanitizer takes care of bacteria, such as those on your skin, and if you have used it frequently over a very short period of time, you may simply have used up the sanitizer in your hot tub, resulting in algae.

Shock Your Hot Tub to Clear the Algae

To take care of the algae, you’ll need to shock your hot tub – hot tub shock is composed of very strong oxidizing agents that can kill off any algae growth. To learn more about shock, we recommend reading our guide to hot tub chemicals. Shocking involves bringing chlorine or bromine levels up to 10ppm. When you have added enough shock, around 50g for a 1000 litre tub, you should leave the cover off for at least 20 minutes to avoid burns to the cover.

You should wait for around a day after shocking the tub before using it, and always test the water’s pH levels before using it. 

Clean Your Filters

When you have cleaned your tub’s water, you also need to clean the filters. To clean the filters, you will need to remove them from your hot tub and rinse it to remove larger particles.

You should also use a specialised filter cleaner to ensure that they’re spotless. If it has been three months or more since you last changed your filter, you may wish to remove the filter and replace it, instead.

Removing Minerals From Your Hot Tub Water

If your hot tub water is green after treating it with shock, then algae is not the issue at hand – it’s likely that metals are leaching into your hot tub’s water. You need to solve this issue quickly, as it can lead to staining, which will be harder to clean off in the future.

The metals that are responsible for green water tend to be iron, manganese and copper. Once the water has turned green, you need to drain your hot tub and then get cleaning. You should drain your hot tub once every three months.

Clean Your Hot Tub

Once the hot tub is empty, you will need to wipe any residue off the surface of the hot tub, which you should be able to do with a damp sponge. The more stubborn bits of residue will require a specialist hot tub cleaner product. Ensure that you wipe the entire interior of the hot tub thoroughly to get rid of all residue.

Refilling Your Hot Tub

Once you have cleaned the hot tub, you should wait for around 24 hours before you refill your hot tub, allowing the cleaning products enough time to dissipate. After this, refill your hot tub. 

If Your Hot Tub Water Is Green, It Can Be Fixed

If your hot tub water is green, it can be a shocking discovery, but it can be fixed relatively easily. You will either need to use hot tub shock to remove algae or drain the hot tub water, clean your tub and refill it. Either way, both of these tasks are a regular part of hot tub maintenance, and so represent good habits to get into.

Green Hot Tub Water FAQs

Is It Safe to Use Green Hot Tub Water?

We strongly recommend that you do not use your hot tub if the water is green. Depending on its cause, it can make you sick, and is, at the very least, not a pleasant experience.

What Colour Should My Hot Tub Water Be?

Your hot tub water should only ever be a transparent blue. If it is another colour, there is something wrong.

What Are Other Signs My Hot Tub Water Is Bad?

Other signs that your hot tub water has issues include a bad smell, mustiness and cloudy water. Keeping on top of hot tub maintenance can help avoid these issues.

Sarah Watkins
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