Green hot tub water can be a common problem, particularly if you leave your hot tub uncovered. Green water occurs when algae grows in the water, tinging the color of the water and making it look slightly like pond water – which isn’t the aesthetic you’re looking for.

On top of it looking unsightly, green hot tub water can be harmful to your skin and can cause irritation, so it is not advised that you soak in the water. They can be odourless, but they can also have a rubbish-like and rotting smell to them, which again, is not in keeping with your ambience!

Here’s everything you need to know about why you might have algae in your hot tub and how to get rid of it – for good. 

Why is your hot tub water green?

There are a few reasons why your hot tub water might be green, and it boils down to these key reasons and factors.

An uncovered tub

Leaving your tub uncovered means that algae has easy access to one of the two things it needs to flourish – sunlight. Algae needs sunlight and carbon dioxide to grow, much like other plants, and so leaving the tub uncovered means the algae has everything it needs to grow and develop!

hot tub cover

Tip – Clean your cover regularly and make sure you put it on when the hot tub is not in use.

Filter broken

A fault or dirty filter is not going to do its job of keeping the bad stuff out of your tub. This means that algae can grow freely without being filtered out of your tub.

Tip – Clean your filter regularly and check that it is in working order.

Not enough chlorine

This is the most common cause, and it is when the pH balance of your hot tub is off, making the perfect environment for algae to grow. Warm, unchlorinated water is exactly the kind of environment that algae will want and need.

Testing hot tub water

Tip – Test your pH levels regularly using test strips to make sure your water is just right.

Cross pool contamination

Wearing swimming costumes and using hot tub accessories that have been in other pools, is a sure way to spread algae. You might not see it, but the bacteria is there, ready and waiting to move into your hot tub!

Tip – Thoroughly clean swimwear and accessories when they have been used in other pools.

How to fix green hot tub water 

Start by draining and then thoroughly clean your hot tub. It is best to use a specialist hot tub cleaner for this, as other substances may be too harsh or not harsh enough to deal with cleaning and cutting through algae. 

Once you have cleaned your tub, clean your filter thoroughly and you may even want to leave this to soak overnight. This is a good opportunity to check whether you need a new filter, or whether the one you’re using is in good working order. 

Now, you can refill your hot tub, although you may want to use a hose filter to remove any added metals from the water, to ensure you’re getting fresh and clean water into your hot tub, minimising the risk of algae reappearing. 

Once it is filled you need to double-shock your tub, This means shocking it once, and shocking it twice. You should leave your hot tub for 24 hours to check that the algae has gone and is not planning on returning.

Test the water’s levels, and add any chemicals you need to before heating it up and enjoying those crystal clear waters.

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How to drain your hot tub of green water 

If you’re unsure how to drain your hot tub, here is a step by step guide. 

Turn off the power supply.

Start by draining your primary valve with a hose, or look at using a dirty water submersible pump, which will be able to tackle the algae as it is being drained. We would not advise using your regular submersible pump, as the algae may collect in it. 

Ensure all of the water is removed from the tub, and that it is totally empty. 

Consider where you are disposing of this water, as you will need sewer access, and cannot use the regular drainage for hot tub water.

Other water issues 

Hot tub scum

Hot tub scum is the greyish ring around the hot tub just above the surface of the water. It is caused by a buildup of dirt, chemicals, lotions, and other things that clings to the edges of the hot tub. You can read more about it here, and you can fix it by cleaning the scum away, or even cleaning your whole tub if you see fit. 

Hot tub water green but clear?

This is a tell-tale sign of algae being present in the tub, even if you can still see the bottom of it. Follow our steps to clean the tub and make sure you shock it twice.

Hot tub water cloudy

Cloudy hot tub water is caused by a variety of things, but the most usual suspect is over-chemicalized water. Make sure you are testing the levels of your water regularly as it can be harmful to spend time in water that is over-chlorinated.

Hot tub water foamy

The pH and alkalinity of the water can cause it to foam, as well as having leftover detergent or soap within the tub. It is best to drain, clean, and refill the tub thoroughly to prevent this from happening again. 

Tips for clean and safe hot tub water

Here are some of our tips to keep your hot tub clean and safe: 

  • Invest in a good quality cover and keep it clean 
  • Change your water every three to four months 
  • Ensure you filter is clean and working 
  • Be careful not to soak in the tub in lotions and perfumes 
  • Clean your swimwear in between uses
  • Regularly test the pH levels of your tub 
  • Keep your hot tub covered when not in use