[Solution] Got Yellow Gunk In Hot Tub ? [Film, Foam] Do This!

Does your hot feel sticky? Noticed some yellow gunk, firm or foam? Does your hot tub water turn yellow after adding chlorine?

Yellow gunk in hot tub comes because of microorganisms and bacteria buildup. On top of being unpleasant, yellow gunk can also severely ruin your experience inside the hot tub.

The last thing you want is to come home after an exhaustive day to enjoy a relaxing time in your hot tub only to find biofilm or slime on the surface. Is there a way out? Can you eliminate the yellow gunk in the hot tub?

We will have a look at everything touching on yellow gunk in hot tub in this article.

Have you gotten your hot tub accessories this year?

Honestly, when I experienced a hot tub for the first time, it was good enough for me. It hasn’t gone a lot before I thought how cool it would be to have a drink in my hot tub, watch a game or bring my food with me. I had no idea people already made things for your hot tub so you can do just that. I have a long list of hot tub accessories that might be interesting to you. Click here to read the article.

How Do I Get Rid Of Yellow Algae In My Hot Tub?

You can employ several strategies to effectively get rid of yellow algae in your hot tub.

Before we dive into a slightly complicated process, as always there are things worth trying to do first such as getting the right chemical to clean up your gunk fast and easy.

Bio Ouster Spa Purge Hot Tub Restoration - Hot Tub Flush, Hot Tub Cleaner for Jets and Tubes, Hot Tub Chemicals, Spa Chemicals for Hot Tub, Spa Cleaner for Hot Tub, Hot Tub Jet Cleaner (Kit)
  • CLEANS HOT TUB INSIDE OUT: Loosens, suspends & purges non-living nutrients such as lotions, sunscreens, cosmetics and other gunk that build up over time.
  • SINGLE-USE JET CLEANER FOR HOT TUB: Stop getting spa cleaners on your hands. Easy-pour spout disperses a perfect measured dose every time.
  • MAXIMUM STRENGTH FORMULA: One dose will treat the portable spa for 3-4 months. Spa water will look, feel and smell better
  • SPA PURGE WORKS ON ALL PORTABLE SPA MODELS: Formulated for today's premium acrylic hot tubs and jetted portable spas
  • BONUS MICROFIBER TOWEL: Includes premium ultra-soft, non-abrasive chamois designed for superior spa finishes.

Now, if that’s not an option for you, then let’s see what else you can do:


The first thing you need to do is to thoroughly clean all your hot tub’s elements. Primarily, change the filter. After that, clean the tub’s cover, skimmer as well as any other part that is not underwater.

In this phase, utilize a strong sanitizer as it helps get rid of all bacteria, making sure you do not leave any behind.


The next step entails shocking the water. This process kills any microorganisms and bacteria. To be on the safe side, shocking should be four times like you would do.

Once you are through with shocking the water, turn on the tub’s jets. Allow the pump water via all its pipes for roughly one hour. You should do all this while the tub is covered.


Flushing is the next step when it comes to yellow flakes in the hot tub. You must flush all the water in the tub after shocking. Draining the water is handy at getting rid of any bacteria that might have accumulated in the pipes.

Is yellow hot tub water safe?

Yellow hot tub water is best to avoid until restored back to its previous, healthy condition.

Light yellow thermal water generally indicates high residual bromine and low pH. This is quite common with bromine spa systems, as bromine can discolor the phenol red used to test pH.

Bromine can discolor the phenol red used for pH testing. The pH appears to be higher than it actually is, often leading to the addition of acid. The higher the bromine level, the more likely the pH test will be discolored,
so it becomes a vicious cycle.

To test the pH of spas containing bromine, use up to 5 drops of chlorine neutralizer to get a more accurate reading. When the pH and total alkalinity are properly adjusted, the yellow discoloration should disappear.

What causes slime in a hot tub?

Biofilm in spas is usually caused by an accumulation of bacteria and microorganisms inside or in the plumbing of your spa. This sludge can make the water cloudy – or worse – it can lead to an odorous, foamy substance floating in the water. Unfortunately, spas are the ideal environment for the development of biofilm because they are generally dark, hot and humid.

However, spas that are not properly maintained and disinfected are even more likely to develop biofilm. Biofilm is usually caused by chemicals in or on the bathing person’s body, such as skin oils, deodorants, hair products, lotions and perfumes. Older or damaged filters, unbalanced water and poor hygiene can also lead to slime formation.

Too much of this slime reduces the effectiveness of disinfectants such as chlorine. It can also clog your spa’s plumbing and harbour bacteria colonies. Once it becomes established, it is very difficult to get rid of, so it is important to avoid it in the first place.

How Do I Get Rid Of Slime In My Hot Tub?

You can get rid of slime in your hot by effective scrubbing. You need to scrub it down thoroughly with an all-surface cleaner. While at it, it is prudent to ensure that you access all parts of the hot tub including the jets and floor.

The rule of thumb at this stage is to make sure that you do not leave any part untouched. Be as thorough as possible. Thorough scrubbing ensures that slime does not grow or find its way back.

Once you are certain that you have handled a thorough scrubbing job, you can fill it with clean water.

Got Problems With Mildew and Algae ?

This also includes mold so if you have these issues, I have a whole new article that helps you get rid of these for good. You can read the article here.

Will Chlorine Kill Yellow Algae?

Yes, chlorine will kill yellow algae. One of the most effective ways of eliminating yellow algae is by using a disinfectant that has chlorine. Thoroughly clean your tub regularly using this solution for better results.

Does Shock Kill Mustard Algae?

Yes, shock is among the most efficient ways of killing mustard algae. You need to use 2 lbs. of shock per 10,000 water gallons.

It is natural for water in the pool to be cloudy or hazy when trying to get rid of mustard algae. Does your tub filter struggle to maintain clear water? If yes, a clarifier is a handy alternative.

While at it, always ensure that the pH inside the water remains to 7.4. Finally, yet importantly, it is prudent to clean your pool daily.

Vacuuming is necessary to eliminate any dead algae.

How Much Shock Does It Take To Kill Mustard Algae?

As we have already highlighted in the earlier section, you should use 2 lbs. of shock per 10,000 water gallons to kill mustard algae.

Shocking kills any microorganisms and bacteria. To be on the safe side, shocking should be four times like you would do.

For impressive results, once you are through with shocking the water, turn on the tub’s jets. Allow the pump water via all its pipes for roughly one hour. You should do all this while the tub is covered.

How Long Does Yellow Out Take To Work?

You should allow Yellow Out around 8 hours for it to work. Of great importance to note is that Yellow Out dissolves once you put inside the water, it is not a herbicide or algaecide. This means that it is poison-free.

Experts recommend that you do not get into your pool after putting Yellow Out as you would after shock or chlorinate your tub.

Why Does Yellow Algae Keep Coming Back?

Yellow algae are notorious for coming back because of an array of reasons, chief among them is improper cleaning. Yellow algae can also come back if you don’t maintain optimum sanitizer, chlorine, pH, and alkalinity levels.

What Does Dead Mustard Algae Look Like?

Mustard algae looks powdery and dry. It features a distinctive yellow color that ranges from brighter yellow to a deeper, dull type. You can mistake it for pollen or dirt.

Yellow algae prefer still water and shade. For this reason, you’ll find it clinging to your tub’s bottom part or the walls.

How Do You Know If You Have Mustard Algae?

You can tell if you have mustard algae by feeling and observing whether it feels slimy. If it feels slimy, chances are high that it is mustard algae. If the feeling feels gritty chances are high that it is calcium scale or dirt.

What Is Mustard Algae?

Mustard algae refer to a chlorine-resistant type of green algae that looks like sand or dirt on the side or bottom part of a hot tub. it has compounds that play the role of a defense mechanism against a sanitizer’s oxidation efforts, thus coming in handy when it comes to surviving excess chlorinated conditions.

Getting rid of mustard algae is easy as you only need to brush it away. Unfortunately, it returns very fast.

Some of the notorious causes of mustard algae include:

  • Imbalanced pH Levels – Low or too high pH level isn’t recommended for your hot tub. Both extremes can cause detrimental effects to the tub, one of them being the formation of yellow gunk.
  • Improper Sanitization – Sanitization is another issue that can bring with it countless negative issues to your hot tub. Some chemicals are better than others. If the chemical that you are using is not effective, it can make you add excess amounts into the tub. Excess use of a chemical can cause the formation of yellow gunk.
  • Metals – Some metals present in your hot tub’s water can cause yellow gunk to form. Some of the most notorious ones include iron, manganese, and rust.
  • Uncovered Tub – Uncovered tub not only promotes the growth of yellow algae but also encourages its multiplication.

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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