Why Is My Hot Tub Water Green? And What to Do About It.




If you swim in a lake or a pond and the water is rather green then most people don’t worry too much about it. But when you find your hot tub water green that is a different matter.

As a general rule, the most likely explanation for what turns hot tub water green is an algae infestation (algal bloom). In addition to having green water, the sides of the hot tub will probably feel slimy too with algae clinging to the surfaces. Algae problems are predominantly the result of too little sanitizer, such as chlorine or bromine.

In this post I will try to help you understand why you may have algae in your hot tub, how to get rid of it and how to prevent it from reoccurring.

Why Is My Hot Tub Water Green

Why might your hot tub have algae

The main reason why your hot tub may be suffering from an algae infestation is that your chemical sanitizer levels are too low. This would be the case for both chlorine and bromine sanitized hot tubs.

You may be adding too little of it when you do or perhaps not adding sufficient. When the sanitizer levels are correct algae may enter the hot tub but will be killed quickly. Also if you have a problem with your filtration system or even a dirty filter that can help algae to get a hold.

Sunlight is a big factor too in the development of algae so if your hot tub is outside, and gets the sun on it, then make sure you keep the cover on when not in use. That will also reduce the likelihood of airborne algae from entering.

Once it takes hold algae can grow at an alarming rate turning a hot tub green almost overnight.

But how does algae get there? Well it is surprisingly easy actually as it can be carried on the wind. Even if your hot tub is indoors, out of the wind it can still get in there, even on someone’s swimwear if they had previously been swimming somewhere that had algae such as a river or lake.

How to get rid of hot tub algae

After an algae attack in a hot tub there are two ways of dealing with it. One is to shock the hot tub water to kill the algae and the other is to drain the hot tub, clean it and refill. Read: How to drain a hot tub.

If you have a severe algae attack then personally I would do both. First shock to kill the algae and then drain, clean and refill. Trying to remove all of the dead algae (known as algae dust), once the shock has killed it, can be quite difficult so you may find it is quicker, in the long run, to just drain it.

How to shock a hot tub

  • First, check that the pH levels in the pool are correct (between 7.4 and 7.6) and adjust as necessary.
  • Using a pool or hot tub shock following the instructions as to how much shock is required for the number of gallons in your tub.
  • Add the shock and leave the pump running (without the air) to ensure the shock is distributed around the tub, including through the pipes.

After a few hours you should see the water start to clear and the dead algae lying on the bottom. When the water is clear retest the chlorine level and add more if required (unless you will be draining and refilling as this would be a waste of chlorine).

Draining and refilling the hot tub

There are numerous ways you can drain a hot tub. I cover them fully in my post How often should you change hot tub water? but basically you can either use a hose (creating a siphon), using a submersible pump or using the hot tub’s drain.

Once empty you should thoroughly clean the hot tub before refilling and then balancing the chemicals.

Is algae in hot tub dangerous?

It is important to know is green hot tub water safe?

Potentially algae can be toxic to humans and pets. These are known as HABs (Harmful Algal Blooms) or Cyanobacterial Harmful Algal Blooms. In some cases exposure to it could cause irritation to the skin, eyes, nose, throat or lungs. Swallowing it could cause stomach pain, headache, vomiting, diarrhea and possibly even liver damage.

So as the CDC says, “If in doubt stay out!”

If you or a family member gets sick after contact with algae, consult a healthcare provider for advice about how to relieve your symptoms. https://go.usa.gov/xQyjw

How to prevent algae in your hot tub

hot tub water green - prevention

The most important thing to prevent algae in your hot tub is to keep the hot tub clean, clean the filters regularly and maintain the correct levels of sanitizer (chlorine or bromine), pH and alkalinity.

Other preventative measures are to make sure you replace the hot tub cover after use, particularly if it is in sunlight. This will not only help to stop algae from entering on the wind but also, as algae needs light to grow, it will keep the light out.

If you or your children could have possibly been swimming somewhere where algae exists (in a lake or pond for example) then make sure swimsuits are properly laundered before wearing them in the hot tub as algae can be transferred on them.

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Why Is My Hot Tub Water Green? And What to Do About It. 1

Does chlorine kill algae?

Chlorine is a great algae killer. Keeping your hot tub chlorine level at between 2 and 4 ppm (parts per million) will ensure that any algae that may find its way into it will be killed before it has a chance to grow.

Your water will therefore remain clear and clean with little or no possibility of having an algal bloom attack.

Will bleach kill algae in a hot tub?

Bleach will kill algae in a hot tub as it is basically chlorine in diluted liquid form. However, the chlorine in bleach it is not stabilized so you should only use it as a shock, not as a regular sanitizer.

You should also be careful that you do not overdo the amount you put in. Perhaps use no more than a cup of bleach to shock the hot tub to remove algae. Make sure that you test the water before anyone uses it to ensure that the chlorine level has reduced to a safe level of 1-3 parts per million (ppm).

You should ensure that you do not use bleaches that contain fragrances or any other kinds of additives (check the ingredients on the label.

Other reasons for green hot tub water

If you are sure that your water isn’t green due to algae ( the sides are not slimy etc) then it is possible for the water in a hot tub to go green for reasons other than an algae infestation. Usually this is usually more of a “tint” to the color of the water than a deep green that you cannot see through, as is normally the case with algae.

The probable reason for this would be high metal content in the water, particularly copper. To remove it you should first ensure that the sanitizer, pH and total alkalinity are correct and then add a metal eliminator such as Natural Chemistry Spa Metal Free to clear the water.

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