Simple: Prevent And Clean Hot Tub From Mold, Algae And Mildew [August 2020]


Most often, hot tub algae, mold, and mildew are common causes for bad smell and it can contain a lot of bacteria along the side. Although a filter can remove impurities from your hot tub, it has no effect on the bacteria in there.

If you need a quick answer to how to prevent and clean your hot tub from mold, algae, and mildew, then here it is. 

The number one reason why you can see and smell mold, algae, and mildew is poor hot tub care. This includes your pH levels being out of balance. Additionally, you probably need to add more chemicals, like bromine or chlorine, that will solve the issue.

Keep in mind that it might be a good idea to drain the hot tub after shocking the water with sanitizer.

Further reading

Are You Also Having Issues With Cloudy Water?

Hot tub mold, algae and mildew are closely related to cloudy water. Dealing with cloudy water will serve as prevention for mold algae and mildew. If you want to find out more details on how to deal with cloudy water and indirectly prevent your hot tub from getting the black and white scum, then head over to this nice article where I have it all summed up.

Black Mold

What Causes Mold, Algae, And Mildew

Even though algae, mold, and mildew are really different organic substances, they can cause equal trouble. In general, algae are categorized as plants, whereas mold and mildew are fungi, and the final decision is that you definitely don’t want them in your hot tub. However, they can be removed and we know exactly how to do it. 

TypeColorTreatmentAffectsCauseNotes
AlgaeGreen – Yellow
White – Black
Hard, SanitizersWater, ShellLow pHLikes Sunlight
MoldWhite, BlackHard, SanitizerCover, Water, ShellLotions, SoapsCheck Jets/Plumbing
MildewWhite, BlackEasy, WipeCove, Water, ShellHumidity and High TemperatureMold In Early Stage

More About Hot Tub Algae

Algae can take many forms in your hot tub water and they can appear in various colors as well. They go anywhere from green to yellow to white to black. 

You may notice that your water turns greenish or cloudy, or that the sides of your hot tub shell suddenly feel slippery to the touch. 

Algae will generally form in a hot tub when the water pH levels are out of balance. Additionally, they show up when there are not enough sanitization chemicals, such as bromine or chlorine. One thing to remember is that the sunlight makes algae flourish, so make sure that you don’t leave your hot tub uncovered for extended periods of time.

More About Mold and Mildew

Mold and mildew usually look like a floating white slime in your hot tub water. They can also take the form of discolored white or black patches on your hot tub shell. 

Filters | White Water Mold

Mildew, on the other hand, is a surface fungus that is usually easily wiped away, while mold might be a sign of a more intensive infestation and requiring a more sophisticated approach in order to remove it. 

Mold is most likely to form in a neglected hot tub that hasn’t been taken care of properly. Usually, it is caused by soaps, lotions, or other substances that have been passed to the hot tub from your skin. Once you recognize the mold on the surface, then it would be smart to check the filters, jets, and plumbing where they also occur and grow. 

It is not rare for the mold and mildew to first appear on a hot tub cover and then spread to the water.

Is White Mold In Hot Tub Dangerous?

All types of mold, including white mold, pose some real health problems and should be treated seriously. You should try to remove the white mold as soon as possible in order to avoid health risks and structural damage. It is known that even milder forms of white mold can represent a health risk.

The biggest problem so far was that some people don’t realize that white mold is mold. This alone may put them at higher risk for an extended period of time. The symptoms caused by white mold include allergic reactions, eye irritations, dizziness, nausea, respiratory infections, headaches, and even mild depression.

In case you notice that you or a family member has been affected by mold exposure, make it a priority to consult a doctor and have the mold removed as soon as possible.

How Do You Get Mold Out Of A Hot Tub Cover?

There is a case where a musty smell has been coming from their hot tub and they always thought it was the water. Here is how they successfully removed it:

  1. Then they checked the chemical levels and it was always within the manufacturer limits. 
  2. They then tried draining their spa every other month but the musty smell always reappeared within two weeks. 
  3. They then discovered that the musty smell was coming from bacteria growing inside the hot tub covers. 
  4. They removed the plastic enclosed foam cover from the liners and found out a large number of bacteria that was growing within. 
  5. Using a simple mixture of 50% water and 50% Clorox they sprayed the cover and then using a small towel, they wiped the entire inside of both liners. There is an important note here: Be very careful when you remove the plastic-covered foam tops from the liners. It is a fact that Black Widows make their home there. 
  6. Make sure to inspect the liners prior to beginning any work for these insects. 
  7. In the end, the cleaning process worked and there was no more musty smell. 
  8. I left the liners hanging overnight to dry out before reinstalling them back over the plastic-covered foam tops.
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  • Quick-dissolving, dual action pool chlorine granules that maintains a healthy pool
  • Pool sanitizer and shock
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  • Improves filter performance

How Do You Clean A Hot Tub Without Draining It?

This is a very frequent question and I feel like it hasn’t been addressed enough. Most of us would like to somehow have a quick cleaning without going through the hassle of draining the hot tub. And this is especially true if you are purchasing a used hot tub.

This is possible but with a condition that you have already maintained your hot tub properly, so now it would be easy to just monitor your pH levels and alkalinity and make sure you use enough chlorine for your hot tub. 

Now This Is How To Properly Prepare Hot Tub For Less Cleaning In The Future

In case you are not familiar with the decontamination, here it is.

Decontamination is the process of Super Hot Tub Shocking to kill and oxidize everything in your tub. There are two reasons why you would want to do this. 

  • The first one is that your hot tub contains an excess amount of organic waste, and as a consequence, it is using large amounts of sanitizer. 
  • The other is that you have bacteria that are actively growing in your hot tub that has formed a protective shield (also known as Biofilm). Having normal sanitation levels will not kill it. 

You could tell about the first one quite easy by simply measuring the sanitation levels, but the latter is a more difficult case and often not recognized until after you start getting sick.

This might sound extreme to some, but I would definitely recommend decontaminating any used tub that you just purchased, especially if you have kids that plan to use the hot tub. 

You cannot be sure enough about how a used hot tub was maintained before you got it. There is no reason to take chances of becoming sick and then spending more on your medical bills than a weekend preparing your hot tub. 

So how do you do decontamination? Here’s how.

  1. You want to start by using an enzyme to clean out your pipes, such as Swirl Away, Spa Flush, etc. When you add this product, keep running the jets for 30 minutes and let sit overnight. It will clean out your pipes and deposit the gunk along the waterline. You should then wipe the waterline with a dry cloth or paper towel. Don’t forget to remove your filter before adding this product. Even better, get a new filter.
  2. Now, the next day, you must definitely drain your tub and then use some of the leftover enzymes from step one to clean the walls.
  3. Then refill the hot tub back as high as possible (above the normal waterline) with fresh water, and then install the filter you bought.
  4. At this point, you want to balance the water. TA = 80 ppm and pH = 7.2. Keep in mind that if your pH is too far out of range, it will lower the effectiveness of the Chlorine.
  5. Then add 50 ppm FC using Regular Clorox 6% Unscented Bleach. That’s approximately 1/4 gal (32 oz) per 350 gal tub.
  6. Run all jets and air features for 30 to 60 minutes. Try turning the air on and off every 10 mins, to help clean the airlines.
  7. Turn the hot tub off and drain the hot tub again. Keep in mind that this water is highly chlorinated, so you may want to keep it away from any plants and food.
  8. While the tub is being drained, use the time to clean the cover and all shell surfaces with the super chlorinated water. Rinse afterward.
  9. Finally, refill the tub with fresh water again
  10. Repeat step 4, which is to balance the water.

After these steps, you want to test your Chlorine Demand to make sure the Decontamination process worked by doing the following.

  1. Shock with Dichlor (Stabilized Chlorine) to 10 ppm FC. Important to know: Don’t use the tub. Simply let the jets run for 10 minutes, cover and let it sit 24 hours.
  2. Check FC. If FC is 5 ppm or above, you should be fine. If it is zero, then your hot tub is still using excess Chlorine, and it really needs to be decontaminated again (Absent the Spa Flush). However, this rarely happens to anyone.
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  • Spa Essentials Chlorinating Concentrate is a spa and hot tub sanitizer
  • Customers prefer this product because it is a fast acting granular stabilized chlorinator 
  • This is a hard-working product that will kill and control bacteria
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Now when you have done it once, your hot tub should be clean like new. As said in the beginning, if you maintain your water properly, you should never have to do this again.

Bonus reading

Have You Mastered Your Hot Tub Chemical Usage ?

It took me some time to collect everything but I was able to gather most of the questions people had about hot tub chemicals in general and published this lengthy article to be used as a guide that you now have access to.

Related Questions

Can You Clean Hot Tub With Vinegar

Whether you want to go natural or simply save a dollar, you want to consider actively using vinegar as a cleaning tool.

When it comes to cleaning the filters, officially, filter cleaners are very acidic, probably a lot more so than vinegar. Still, a lot of people can’t see the difference when using it.

As for the smell. Vinegar washes out of just about anything very easily. People have found that vinegar works much better as a general-purpose cleaner rather than most of the bottled cleaners.

Generally, vinegar is really effective against mold and mildew. What you can do is get a mixture of 50% vinegar and 50% water. Identify the area of the cover on which the mold is growing, and then spray the mixture on it. Spray enough so that it covers the entire layer of mildew.

Can I Use Bleach To Clean My Hot Tub

Well, you shouldn’t use bleach, but you could use dichlor. Let me elaborate.

Bleach and dichlor will both get you to the same place, just one having drastically different side effects. They are both categorized as chlorine, just manufactured in a different way.  

Bleach is sold at pool stores and usually comes in double strength to be used as liquid chlorine or liquid pool shock. This bleach is not any different than the one you buy at the local grocery store, assuming that you are buying straight, unscented bleach.

All chlorines have their pros and cons.  For example, bleach has a relatively high pH. It is difficult to transport (liquid) and loses strength over time.  These are the exact reasons why it is not recommended for use in a hot tub. Bleach is the closest to the pure chlorine, has relatively few byproducts and is almost all water.  We generally use bleach in our washing machines and commercial dishwashers amongst many other uses.

Dichlor, on the other hand, has a relatively neutral pH and is easy to transport (quick-dissolving granules). This is what makes it recommended for use in hot tubs, especially by the spa manufacturers. It is nearly 50% by cyanuric acid (aka pool stabilizer) which will build up in the spa water (especially if you shock with dichlor) and reduce the sanitizing ability of the chlorine over time.

Now if you want to explore more, there are others such as lithium, cal hypo and trichlor where all of them have the particular qualities that make them acceptable in certain uses and not so in others, but they all are the same basic chlorine.

Most people would never recommend bleach as a primary sanitizer. They would only suggest it in order to get the ppm level up that high and that quickly. It is the cheapest and easiest solution out there.

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Editorial Staff

I'm Adnan Sabanovic, the guy behind Hot Tubs Report. I've had a chance to enjoy hot tubs last few years and have really become interested in owning one of them. Nearly every weekend you'll find me spending time with my family or playing sports. If I am not doing that then I'm here writing about tubs on Hot Tubs Report. This blog is a research for my first hot tub which I decided to document and share publically so others can benefit from it as well.

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