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Common Hot Tub Issues Why is my Hot Tub Water Green?

Ok, so we’ve all been told to ‘Stay Home’ and while admittedly this can be difficult, stressful and sometimes even anxiety producing, it also provides a good opportunity to hit the pause button on our otherwise fast-paced and hectic daily life.
As a hot tub owner, your back garden can easily become a peaceful place to relax and rejuvenate, especially when the house feels extra crowded and tensions are running high. However, if your hot tub water seems to have lost its sparkle, you may want to take this extra free time and use it to give your spa a little T.L.C.

There’s nothing more uninviting than dull, murky coloured water, and green water can be a particularly alarming sight for hot tub owners. However, green water is nothing to be overly concerned about. It is usually caused by mineral content in the water and can be treated fairly easily. In this article we explore some possible causes of green hot tub water and learn how to identify and treat them.

Possible Causes



Algae is not the most common cause for green water, however it is certainly possible. The reason alge is not a common cause of green water in hot tubs is that it needs sunlight to grow. Since hot tubs are usually covered with an insulated cover when not in use, it can make it difficult for algae to thrive. Yet, in the right conditions, algae can grow and spread quickly when the spa is left uncovered.

What are algae?

Algae is the plural noun of alga. Algae is a broad, informal term used to describe many types on non-flowering aquatic plants, usually green in colour. Alage are photosynthetic organisms, which means they absorb light ans transform it into energy. Alga is also an eukaryotic organism, which means its cells share similar characteristics to those of plants and animals.

How do I know if it’s algae?

If algae is the cause of green spa water, you should be able to feel a slimy coating on your spa’s shell, particularly around the tide line. If the water is green but there is no slimy coating, this could mean the colour is down to another cause such as high mineral content.

How do I treat algae growth?

The treatment for algae will depend on the severity of the growth. If you’re dealing with a mild case of algae, shocking the hot tub may be sufficient enough to kill it off, however we recommend fully draining and cleaning the spa to ensure no spores are left behind and the plant can continue growing.

Before draining, be sure to shock your hot tub using a spa shock treatment and run the jets. This will help clean out any spores within your hot tub’s pipe work, preventing it from contaminating your clean water. Once your hot tub is drained, you will need to thoroughly clean the shell. We recommend using a spa surface cleaner to do this, you can also use a properly diluted bleach solution which will help to kill any remaining spores and bacteria. Take care to remove headrests and nozzle caps if possible and clean behind these. Refer to the manufacturers guidelines when cleaning removable components to prevent damage or corrosion.

Before refilling the spa, be sure to remove and clean the spa filters.

Finally, once you have refilled your hot tub with clean water, shock it once again and run the jets to ensure any remaining spores are eradicated. Use your chosen sanitizer to treat the water and check and adjust the PH balance using test strips and PH plus/minus solution.

How do I prevent algae growth?

As is usually the case, when it comes to algae growth, prevention is cheaper than the cure. To help prevent algae growth in your hot tub, make sure your spa’s sanitizer levels remain topped up and PH levels remain balanced at all times. Low sanitizer levels and imbalanced PH are prime causes of bacteria growth including algae. Remember, algae thrives in sunlight, so try to keep your hot tub covered whenever it is not in use, and try not to leave it uncovered in direct sunlight for too long, Especially if you are treating algae.

Mineral Content

Although it is less likely green hot tub water can also be down to the presence of certain minerals such as copper, iron and manganese. These minerals can make their way into your hot tub via your water source.

It is important to treat the problem as if left ignored it can cause staining of your hot tubs shell, as well as corrosion of pipe work and fixtures such as nozzles.

How do I Know if minerals are the problem?

If there’s no slimy coating around the shell, your sanitizer and PH levels are balanced and your hot tub has not been left uncovered, it could very well be a high mineral content causing that green tint.

If copper is the culprit, the water will tend to have a more vibrant hue rather than a dull, murky green. However, if it is a combination of metals the water could be green with an orangey/rusty hue (iron) or even a purple/brown tone (manganese).

How do I treat high mineral content?

Shocking your water or trying to treat the problem with chlorine will only oxidize the metals and make the problem worse. Instead you will need to use a sequestering solution designed to remove metal content from hot tub water. Sequestering agents bind minerals together, preventing them from becoming oxidised and allowing them to be removed through the hot tub filter.

How do I prevent high mineral content?

High mineral content makes its way into your hot tub via your source water, thus preventing minerals from entering your water may not be easy. However, treating the water once you fill your hot tub with a suitable sequestering agent, should be enough to rid your hot tub of metals through the filter. Once you add the sequestering agent, make sure to wait the maximum time as directed on the bottle before adding sanitizer. This will allow the sequestering agent to do its job and prevent the metals from becoming oxidised.
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