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Spa Slime and Odor Problems

The result or poor sanitation and/or water chemistry.
The Pool and Spa Informational Website or

Causes, Suggestions, Treatments and Solutions.


Scroll down to browse through some archived SPA and Hot Tub questions and answers.  Please click the Spa Problems Link, on top of every page, to access a complete listing of Spa and Hot Tub Problem subjects, an alphabetized Website Table of Contents, Spa and Hot Tub Equipment Information, About Alan Biographic Material and a Spa and Hot Tub Glossary. Use the other links to access additional subject information. More information about some new and unique products, for Spas and Hot Tubs, can be found by visiting The Website Store. You'll never know what you'll find and that's always fun. Be better prepared and avoid costly problems!


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Managing problems. with Odor and Slimes, in Spa water!!!
Odors and the formation of underwater slimes are usually the direct result of inadequate sanitizing and/or poor water chemistry.  Sanitizing and water chemistry are important, for proper spa water management.  Salt Chlorine generators are a better way to utilize chlorine, producing more controllable and better results, with greater convenience. They eliminate the need to handle, measure or store chlorine products, while reducing buildup problems.  An Electronic PockeTester Kit is a convenient way to monitor the salt level.
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SmarterSpa Salt Chlorine Generator, with Chlorine Detection Technology. #1749 PockeTester Kit, for salt TDS and temperature. MegaChlor-CD salt chlorine generator, with Chlorine Detection Technology.
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If you have a pool or spa water testing need, we should have the product.
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To achieve better sanitation and reduce odors, proper water chemistry is required.  A ColorQ 2X is a 2nd generation, Bluetooth, Waterproof, all-digital tester, that can measure all the common test factors. There is a model, for every sanitizing need.   If you have a cartridge filter, The Blaster Automatic Filter Cartridge Cleaner will make that chore much easier.  Fine particles can pass through many filters.   The WaterLink SpinTouch Labs are the ultimate tester, doing up to 10 different water test factors, in just 1 minute.  Voted product of the year.
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#2086 ColorQ 2X, Bluetooth, Waterproof, 2nd generation all-digital pool and spa tester. Automatic Filter Cartridge Cleaners, for pools and spas. WaterLink SPIN Touch Lab
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If you have a pool or spa water testing need, we should have the product.
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How to treat and eliminate spa slimes and odor problems?

Slimes are films of microorganisms, usually bacteria or algae, that can be found on the underwater surfaces of inadequately sanitized spas and hot tubs. Biofilm is another common phrase. That slippery, slimy feeling on underwater spa surfaces, especially those in hard to reach spots, is evidence of this problem. Proper sanitation and circulation of the water will eliminate and prevent this problem. Microorganisms can be associated with the development of spa water odor problems. However, odors can result from chemical conditions, especially very low pH and high levels of chlorine and/or bromine.  When using shock, the label doses are only a guide. Your spa or hot tub could require more or less, depending upon the actual water quality. If problems arise, refer to the Spa Problems Page, as a source of problem-solving information, broken down into various categories.  Scroll down the page and click on the linked keywords, catch phrases or images, in the archived answers below, to access additional information, on that topic or product.

Do you know what's in your water?  If you're having problems, with sanitation or water clarity, testing allows you to better understand the chemistry and determine the cause of the problem.  Once understood, you can select the best treatment option.  Understanding the nature of the problem, should be step one.  For information about our full selection of testing options, visit our Test Equipment Store.

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▼     Helpful, Problem-Solving Information, in a question and answer format.     ▼

Slimy Underwater Spa Surfaces?

I have had my spa for 2 years now without any problems at all. But in the last few weeks, I have noticed a white slime covering the filter cartridge. The cartridge is cleaned every 3 uses and changed regularly too. Measured chlorine granules are added daily as per usage guidelines. What could be causing the slime? It's a white/transparent colour and looks very much like Vicks Vaporub. Any idea what may be causing this?

Niki U, 4/17/2020

SLIMY USUALLY MEANS INADEQUATE SANITATION. AND RESULTS IN THE FORMATION OF BACTERIAL SLIMES.  Going forward, you have to pay more attention to the free chlorine levels or supplement with an ozonator or mineral sanitizer.  Spas should be drained and cleaned every three mSmarterSpa Automated Salt Chlorine Generator.onths and this would seem to be a good time.  Add a gallon of liquid laundry bleach and keep recirculating, until the slime is gone, repeating if necessary.  Then drain and clean.  The filter should be replaced, of cleaned by soaking it a plastic bucket, filled with water, to which 8-ounces of bleach, per one gallon of water has been added.  Always add the bleach to the water.  The use of stabilized chlorine has come under rebuke, by health authorities and industry experts, as its use will inevitably cause the level of cyanuric acid to rise.  This causes the chlorine to becomes less effective, requiring higher and higher levels of free chlorine to maintain proper sanitation.  If you're going to use chlorine, then a salt chlorine generator is the better way to do it, as it will eliminate buildup problems and provide better results and more control.  We offer 4 salt chlorine generators, that require no installation, and two of them are "smart enough" to only produce chlorine, when it is actually needed.  I hope that this information is helpful.

Sincerely,  Alan Schuster. 4/17/2020

Slimy, Dirty Spa Water?

I can't seem to get my hot tub water right, I keep getting slime and the water is cloudy like dirty bath water and I hardly use it because of this. I am at my wits end on what to do.  Thank you.

Selena, 11/10/2019

SLIMY USUALLY MEANS INADEQUATE SANITATION. Spas should be drained periodically and this seems like a good time. I would
#2086 ColorQ 2X - 2nd Generation Pool/Spa Testeradd a gallon of laundry bleach, at a time, until the slime is gone. Then drain, clean and refill.   However, you are sanitizing is wholly inadequate and may be being made worse, by not testing the water often enough. The only thing that keeps the spa water, from becoming old bath water, is proper sanitation. Unless you pay more attention to the sanitizing regimen and the water chemistry, you will never be happy with the results.  A salt chlorine generator is a better and easier way to sanitize a spa. We have 4 models, that require no installation, and two of them are smart enough to only produce chlorine, when it is actually needed. They operate independently of the pump and filter and will greatly simplify maintenance.  Want a better way to do a complete test water analysis? The ColorQ water analyzers are all digital, use no look up charts and completely eliminate all color matching and guesswork. You will find ColorQ Testers for spas or hot tubs using Chlorine, Bromine, Copper Ionization and Biguanide. There's one just right for your spa.  I hope that I have been helpful. If so, please tell your friends and dealers about the website.

Sincerely.  Alan Schuster, 11/10/2019

Spa Odor And Irritation With Biguanide?

There is bad smell in the tub that burns your eyes and mouth and it leaves a stinging taste on your tongue. The tub sits outside with a cover, the water is clear. We use all of the biguanide spa chemicals.

Tom F., Winona, MN, 3/2/2018

ChlorMaker Drape-Over Salt Chlorine Generator, for spas and swim spas.
Proper use of the chemicals should not be creating such problems. I suggest that you bring in a water sample into a local spa
professional. Low pH conditions could be a cause of the odor problem and irritation. In addition, biguanide can lead to the development of resistant micro-organisms. When that is the case, a permanent switch to another form of sanitation is required or the problem will return time and time again. Salt Chlorine Generators, Ozone Generators and Mineral Sanitizers are some excellent, alternative spa sanitizers. I hope that I have been helpful.

Sincerely. Alan Schuster, 3/2/2018

Natural Treatment?

We have had our spa for about a week now. As of yet we have not added any chemicals to it, but the water is starting to get a bit cloudy and smelly. We are not too keen on the idea of using chemical cleaners/purifiers and wondered if we could just use pure rock salt instead. Would that be any good. Thanks.

Jan C., 10/12/2015

SmarterSpa complete unit
Without the addition of sanitizing chemicals and an oxidizer, your spa will become dirty old bath water. Rock salt is useless! You need to add a sanitizer and/or oxidizer and get the overall water chemistry adjusted.  There are lots of sanitizers to choose from and I suggest that you browse through the website. Choices include: chlorine or bromine, ozonators, mineral sanitizers, ionizers, salt chlorine generators and ultraviolet sterilizers. Some can be used in combination to help reduce the chemical presence and make maintenance easier. Unless you do something, your spa will not be fit to use. If unsure, bring in a water sample to a local dealer. I hope that this adv ice will help get you on track.

Sincerely. Alan Schuster, 10/12/2015

Slippery Surfaces?

Every now and then there are certain areas of the spa that seem to be slippery. I've been using bromine in a small floating cartridge. The pH is 7.6, bromine 2.5, the alkalinity is 112 ppm and the water looks clear. What's causing the slippery feeling. Thank you.

Nameless, 11/2/2011

What you are describing sounds like a bacterial slime. Simply stated, that slippery, slimy feeling is a film of bacteria. Your water chemistry seems reasonable, although, the optimum range for bromine is 3-5 PPM. But what was the bromine level yesterday? I suggest that you shock the spa with a quick acting product such as a non-chlorine shock. Boost the bromine readings above 5.0 PPM and keep it there, until all traces of the slime is gone. Keep the filter running during this period. Thereafter, resume a bromine level of 3-5 PPM. Test the spa water before each use and add shock, if the bromine level is too low. After periods of heavy bather use, test the water and add additional shock, as might be required. The bromine, in the floater, is slow dissolving and the addition of shock is a way to quickly boost the bromine level. Keeping a proper bromine level should prevent a recurrence of the problem. Having an ozonator will make it easier to maintain a proper level of bromine and make problems, such as you have described, mush less likely. I hope that I have been helpful.

Sincerely. Alan Schuster, 11/2/2011

Uninvited Guest?

Yesterday morning I found a piece of a large earthworm in our spa. I found the other pieces in the filter. I'm not exactly sure how it got in there, but I'm fairly certain it happened the night before. The earth worm didn't smell too appealing when I took it out and it seems that this smell had been transferred to the water and filter. My question is, will shocking be sufficient to remove any unwanted organics left behind by this partially decomposed creature or should I drain and refill the spa? I had just refilled the spa 3 days prior to this incident and didn't want to do it again unless absolutely necessary. Thank you.

Ken G., 1/2/2014

The earthworm smells like the decomposing animal that it is. Shocking the spa will destroy all of the organic contributions and odorous products. There is no need to drain and start over. This is a fairly common thing in a swimming pool, as it can be at ground level. Enjoy the spa and I hope that I've been helpful.

Sincerely. Alan Schuster, 1/2/2014

Musty, Moldy Spa Odor?

Let me start by saying this website has been extremely helpful. My wife and I just purchased our first house and on the back porch sits a nice spa. It holds 230 gallons. I spoke with the previous owner and asked them what type of maintenance they performed on the tub and how they took care of their water. I was told that they didn't very much to it and they changed the water every six months. When I asked them what type of chemicals they used, I was told they used no chemicals, because they didn't like what the chlorine would do to their skin. Now, at that point I had no idea but after reading through this site I'm rather afraid of what might be growing in there. When I remove the cover the water looks fairly clear and it smells musty and moldy. Should I sanitize before I drain the water? How would I go about sanitizing. In the near future I plan on purchasing an ozonator and mineralizer to handle the sanitization. Thanks in advance.

Luc, 3/3/2017

SmarterSpa Automated Salt Chlorine Generator.
I believe that you better off starting with a clean slate.  Drain and clean the spa and add a healthy dose of chlorine.  Boost the free chlorine to about 10 PPM.
Run the filter for an hour or two and if there is still free chlorine present, you be good to go.  A properly maintained spa should be relatively free of odor. I prefer using a sanitizer that can be measured. An excellent way to sanitize the pool and the spa is with a salt chlorine generator, which will produce chlorine right in the spa. There is no need to add a separate oxidizer and it is highly automated. This is a complete sanitizing system. Fewer chemicals to add and store, fewer chemicals building up and conditions that are less likely to lead to heater corrosion. Natural is great, but not necessarily for every spa situation, especially not in a small spa, such as yours. I hope that this information will prove helpful.

Sincerely. Alan Schuster, 3/3/2017

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Strong Chemical Odor?

I always seem to be adding pH reducer to my spa The pH seems to be very high. The TA is too low. I use bromine tablets in a floater and the spa has an Ozonator. The problem is there is a very strong chemical odor. We would like to use the spa, but am afraid. What should I do?

H.L., Lanham, MD, 4/14/2009

I suspect that the cause of the odor is that the pH is really too low. I'll bet that it is below 6.0. The problem is that the test kit,
WaterLink SpinTouch Tester, for pools and spas. you are using, is not properly formulated to test the pH, in the presence of bromine. The phenol red could be reacting with the bromine and turning a deep purple color. This makes it appear that the pH is too high. In fact, it can be too low! You should rarely if ever have to add a pH reducer to your spa. If anything, you have to add a pH increaser. I suggest that you bring in a water sample to a local spa professional and get the water tested. The low pH is capable of producing and contributing to the strong odors that you are describing. Over production of ozone could be an additional factor. However, I'd bet on the low pH. Make sure that you use a test kit that the dealer knows will work with bromine.  For your own testing a ColorQ all-digital water tester, would be an excellent choice. To better assure proper overall spa water chemistry, visit a pool/spa store that has a very reliable, professional lab such as a WaterLink SpinTouch Lab, rather than a less accurate test kit or strip reader.  I hope that this information will help get you back into the water. Good luck.

Sincerely. Alan Schuster, 4/14/2009

Unpleasant Spa Odor?

I have had a spa for 6 months. I use bromine tablets in the spa and keep the pH where it should be. My spa always has an odor, that smells like chemical, and it is not very pleasant. If you get your hair wet with the water, it is very difficult to get rid of the smell from the hair. The filter has been cleaned with liquid chlorine. Also, is it possible to drain the spa for the winter and not have any damage to it? What would I need to do?

Jenna S, NC 1/3/2015

A properly maintained bromine spa should be almost free or odors. Certainly free of objectionable levels of odor. Two possibilities come to mind. One is that the bromine is interfering with the pH test and your pH is actually very low. I suggest that you have the pH tested by another method and or dealer. Bromine tablets are acidic and you should have to add pH increaser on a regular basis. Is this the case? The other possibility is that the bromine level has been maintained at too low a level and that microorganisms have taken advantage. Bromine tablets are slow dissolving and do not play catch up very well. On a regular basis and whenever the bromine level bottoms out, you should add a dose of shock: monopersulfate or sodium dichlor. Having an ozone generator on a spa can greatly reduce chemical requirements and improve the water quality. If, as I suspect, your spa does not have one, you might consider adding one. It is possible to drain a spa for the winter. Just be certain that all the water is completely drained. Water in the pipes could lead to freeze-thaw damage. You can drain the spa for the winter. However, you must make sure that all the water is completely drained. Otherwise you will risk freeze-thaw damage. You might have to add some propylene glycol antifreeze to protect the water that remains in the pipes. I hope that you will find this information helpful.

Sincerely. Alan Schuster, 1/3/2015

Fuming And Milky White Water?

We have a customer who recently added bromine tablets to her Spa. She had not removed any water from the spa and had used other brominators in the past. She discovered her spa was producing a "milky white" water when the jets were on. There was a lung searing fumes coming off the surface of the water. I believe this was a bromine fume? Test strips indicated high everything. Any ideas as to what the problem might be?

Ken B., Cody, WY, 3/4/2007

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High levels of bromine can interfere with the pH test and make it seem like it is off the char
t, on the high end. In fact, this purple color has nothing to do with the actual pH. I suspect that the pH is low and this can cause fuming. In addition, the low pH could be releasing scale from the plumbing and clouding the water.  The best way to test high bromine or chlorine levels is with a product such as the LaMotte Insta-Test strips. However, very high bromine levels may still interfere. If you have some chlorine neutralizer chemicals or reagents, add some to the test sample before testing the pH. The homeowner should not have had to add any pH decreaser, as bromine tablets are acidic. Ask if pH lowering chemicals were added! I hope this helps find the answer.

Sincerely. Alan Schuster, 3/4/2007

Masking A Spa Odor?

Are the spa fragrance products effective at masking a chemical odor?

Jane B., 1/4/2006

A spa that is being properly maintained should not have an overwhelming chemical odor. The spa fragrance products are intended to create a pleasant aura about the spa, with the use of an assortment of scents. Use the product to stimulate a mood and not to mask, what would otherwise be considered, an odorous spa water problem. Cosmetic bath or fragrance products should not be used in a spa. I hope that I have been helpful. Enjoy the spa.

Sincerely. Alan Schuster, 1/4/2006

Burning Spa Odor?

I would like to know why when I turn my air valves on when jets are blowing the tiny air bubbles smell and taste acidic. They burn our noses and make us sneeze. It's difficult to breathe. My sanitizer, pH and alkalinity all seem in check with the test strips. Could the pH be just a little too high or low or is there something else involved? Is there some agent I could add to eliminate this? Truly.

Dean, 10/8/2005

If your spa is equipped with an ozonator, you may be smelling ozone. Although, I would not describe the odor of ozone in those terms. If you have an ozonator make sure that it is not producing too much and it is not producing any ozone when bathers are in the spa. Ozonators are usually switched off automatically, when the pump is on high speed or can be controlled by a timer. If you don't have an ozonator, it is possible that the odor is due to low pH conditions. If you are using bromine, it is possible that you are getting a false high pH reading and that your pH can be very low. If you are using bromine tablets, you should rarely ever need to add pH reducer! If you have been adding pH decreaser, your pH testing is probably wrong.  I suggest that you have a dealer test the water. Adding a drop of chlorine neutralizer solution, to the pH test vial or water sample could eliminate the possibility of a false reading. I hope that I have been helpful.

Sincerely. Alan Schuster, 10/8/2005

Cabbage-Like Odor?

I searched through the archives and did not find an answer to this specific question. I am meticulous about maintaining our spa, and for the first time there is a cabbage or rotten egg-like smell coming from it (after my son and his friends used it). I shocked it, adjusted the pH, and got the bromine levels at the desired level. Everything seems in balance, but the smell is still there. What might be causing this? Thank you for your assistance.

Cathryn F., 2/18/2007

The odor could be indicative of a sulfur compound. There is no obvious reason it should have happened. Spas should be periodically emptied, every 3-4 months and this might be a good time.  You may not have all the facts and this course of action makes the most sense.

Sincerely. Alan Schuster, 2/19/2007

White Slime?

I have a 250 Gallon SPA that is one month old. I use Bromine in a floater and the level using OTO is 3.3, pH is 7.2. The problem is an off white film at the top of the water line and it also collects on the floating bromine ring. When the jets are turned on, the white stuff collects in the bubbles and looks like dry wall dust. What might I have and how can I treat the problem? Only 2 of us use the SPA a few times per week. I use a weekly water enzyme additive, Non Chlorine SPA shock every 3rd day and test the water every other day. Thanks.

Joe V., Ohio, 8.15.2005

SmarterSpa Automated Salt Chlorine Generator.
There is nothing that points to an obvious cause. However, the presence of the slime, seems to confirm that you extended periods the sanitizer level
is inadequate. You should add more tablets to the floater and never allow them to completely dissolve before adding more! I suggest that you add a quick solving chlorine and boost the level to 5-10 PPM. Keep it over 5 PPM for an overnight period. From this point forward, make a greater effort to keep the floater filled with tablets and add a small amount of shock, before and after each use. Test the water often and before use, to be certain. You might consider adding a salt chlorine generator. It will help produce better results, especially in a small spa, such as yours. I hope this information proves helpful.

Sincerely. Alan Schuster, 8/16/2005

Startup Odor Problem?

My hot tub was setup by the dealer after being out of service for a year due to me being out of country. After a month in service I changed the filter using a filter that was in the shed for a year but cleaned before I left with a solution from the dealer. After about 24 hours my water turned gray and smells really bad. I contacted the dealer and they said I have a bad case of bacteria and that I should shock the tub, but they don't have any shock. Is there another way of clearing up this problem so we can use the tub? Thanks.

Brian S. 3/13/2013

SmarterSpa complete unit
It is not clear from your letter, if the odor and appearance appeared right away or after a period of time. In either
case, this seems like inadequate sanitation. You need to add a dichlor or non-chlorine shock and boost the free chlorine level to 5-10 PPM. Keep the filter running and make sure that some free chlorine remains after at least a few hours. Otherwise, add more shock. A dealer that does not have shock treatment is not a spa professional - find one that is! Make sure that the pH is 7.2-7.8 and that an adequate sanitizer is maintained. You have to start a chemical regimen to keep the spa sanitized and looking good. A salt chlorine generator will reduce the need to add shock and will provide better control and results. will make maintenance easier and help assure proper water quality.  I hope that I have been helpful.

Sincerely. Alan Schuster, 3/14/2013

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