Moldy Hot Tub Covers

Well, just the title of this article sounds gross because no one likes mold, but unfortunately it is a problem that is encountered far too often by hot tub owners, many who don’t even realize that is they may have a mold problem.

It is very important to clean your hot tub cover regularly to not only avoid dirt and dust build up but also mold and mildew growth. Dirt and dust on your cover may not seem like a big deal as it really does not affect your cover, but it will affect your hot tub water. Dust and dirt build up on your cover will eventually transfer to your water which will in turn cause bacteria to grow in the moisture and build up on the bottom side of your hot tub cover causing mold and mildew growth.

When mold and mildew build up in your cover it will eventually cause the cover to stink. We often hear from customers who state they are doing everything right with their water but are still getting the awful smell. If you are changing your water every 3-4 months, cleaning your filters with Filter Cleaner, and balancing your chemicals regularly chances are the smell is coming from our hot tub cover due to mold.

In this case your hot tub cover needs to be cleaned. This can be done with a cover cleaner mixed with water, it is not recommended to use household products on your cover as they can get into the water and cause problems with your chemical balance. The only exception to this would be if there are physical dark or black splotches of mold that you can see.In this case you can use bleach diluted in water to wipe the cover down, this will help kill the mold. You may also want to remove the vinyl from the cover and wipe down the foam core to ensure the mold is removed.When you are done with the bleach solution be sure to rinse everything VERY well with clean water to ensure there is none left that may cause problems in your tubs water.

Once your problem is taken care of the only way to be sure to avoid the problem again in the future is to clean the cover regularly (approximately every 2 months) by using a cover cleaner solution and water, this will also help extend the life of your cover and keep it mold free.

15 thoughts on “Moldy Hot Tub Covers”

  • Tony

    Thanks for the article. I have a small amount of black colored mold growing on the bottom side of my spa cover. I'd like to use the bleach and water mixture. What ratio of bleach / water would be best. I'd like it to be strong enough to do the job, but not so strong that it damages the cover.

    • hottubwarehouse
      hottubwarehouse May 12, 2013 at 2:15 pm

      Hi Tony,
      Thank you for asking. There is really no specified amount of bleach to water ratio, just diluted. I would just recommend removing the cover from the tub completely when you go to clean it to ensure none of the bleach enters your water. I would then mix the bleach/water in a bucket and apply to the affected area with a cloth. After scrubbing it clean, be sure to rinse it with water only when complete to ensure that there is no bleach left on the cover. We then recommend regular cover cleaning with either Spa Cleaner or Spa Cover Cleaner. Please let us know if you have any other questions.

  • Verena


    We have the same problem with mildew and we're fixing that today.
    My questions are: you mentioned cleaning the cover about every two months; we are in a 4 seasons area, so how would you handle cleaning the cover during the winter months and how do we prevent water from getting into our hot tub during the summer that aides in mildew growth?
    We moved into this house last year at it already had the hot tub. We are new/novice hot tub owners, and shut down the hot tub during this summer to see how much savings it would be. The tub is outside "in" the deck. Water got in, obviously, during rain storms.

    • hottubwarehouse

      Thank you for the inquiry Verena.
      If winter is particularly bad and it would be difficult to clean the cover as recommended, I would make sure to do it thoroughly at the very beginning of the season and then try to at least wipe it down every 2 months (weather permitting). A good hot tub cover should keep rainwater out pretty well if your cover is allowing water into the tub it may be time for a new hot tub cover. On new spa covers we also offer an add on option for a spa cover cap, basically a durable woven polyethylene cap that goes over your cover to protect it, sounds like something that may benefit you especially during the months your hot tub us shut down. Please let us know if you have any other questions!

  • david

    What about black mold that is also forming in the creases of the spa waterfall and control levers? all above water. is a bleach solution really that bad for the spa water? Wouldn't it dissapate?

    • hottubwarehouse
      hottubwarehouse April 17, 2014 at 10:15 am

      Bleach won't hurt your spa since the active ingredients are usually around 3% chlorine if you are using a store bought brand. The problem is that it can bleach your spa cover. The spa surface cleaners are generally more powerful and won't harm your spa or their surfaces.

  • Peter

    I emptied my spa for the summer months (Florida) and was away for 2 months. Upon return the spa cover was covered in mold or mildew as well as the inside. Also, some water seeped into the spa from the rains. I cleaned up the cover alright with a bleach dilution but still have some brown stains on the underside of the cover that won't come out. How can I remove these brown stains? Thanks
    Also, should I have kept the spa full of water and running while I was away to prevent the interior cover stains?

    • hottubwarehouse

      Depending on how bad the stain is it may not be possible to completely remove them at this point. I would try Spa Pure Spa Cleaner which is great for tough jobs.

      It may have prevented the staining if it were left full and running. You can get mold and mildew buildup with it running but it doesn't harden since it is warm and moist.

      I hope this helps, please let us know if you have any other questions!

      • Ron

        perhaps try OXYCLEAN to remove the stains??? What about using the water conditioning bromine tablets dissolved in water or shcok dissolved in water to kill the black mold on the cover (top or bottom side)?

  • Aileen Beehler

    We are closing our hot tub for the winter we dran it and do all your supose to do . Do you leave air space between the cover and the tub so air circulates ?????? I have 1/2 in styrofoam in between the tub and the cover , hopefully that will do the trick . We did not put air circulation remedy be for this is the first time , and loosen the straps to hold the cover down , you think this will help ??

    • hottubwarehouse

      Thanks for the inquiry,

      You don't need to leave an airspace so the air can circulate during the winter. It won't necessarily hurt anything as long as it isn't a large enough cap to allow moisture in. The only other concern with leaving the straps loose to allow air flow is that if the spa is in an area that can see strong winds it could lift up the cover enough to allow enough leverage from the wind to break the strap or buckles. This could send your cover flying.

      Hope This helps, please let us know if you have any other questions.

  • anamddx

    Is there a better designed cover available anywhere that does not attract or harbor mold so easily?

    • Kasey

      Most covers seem to be designed pretty much the same and I am not currently aware of a material that they could use for a cover to fend off mold. Properly balancing the chemicals and cleaning the cover on a regular basis is what we would recommend to fight moldy covers. Thanks for the comment!

  • christine

    Hi , i got a new cover last year and i been having black moldew problem with it .. the straps are not a the same place so i do not use them and the spa is under a roof and 3 wall kind off inclose the other cover never did that
    thanks for your help

  • Tara

    Can you recommend a cover cleaner? I searched amazon and nothing specifically says "cover cleaner".

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