Just as you’re about to immerse yourself in the sheer bliss of your hot tub, you discover an unwelcome sight: Mildew.

Or worse, mold.

It’s what happens when warm water meets fungus.

Microscopic view of mold particles


Mildew is a fungus that commonly grows in damp, humid environments with poor ventilation – like under your hot tub cover, the area between the waterline and hot tub cover or in the folds of hot tub pillows.

Mildew generally looks like a white or gray coating on surfaces. Usually harmless, mildew can smell, cause discoloration, or trigger allergies or respiratory issues in some people.


This is also true for mold. Mold is also a fungal growth. There are many different mold species that come in many different colors. Mold multiplies by producing microscopic spores that are like plant seeds. Mold spores can take hold, grow, and cause health issues and other problems to your hot tub.

It’s not uncommon to occasionally see mildew or mold above the hot tub’s waterline or on a hot tub cover or pillows. It likes to grow in warm, humid environments that don’t see the sun, which sounds like everything under the hot tub cover!

Mold reproduces by producing small seed-like spores. The spores look for porous surfaces, like the hot tub cover, pillows or filter.

The most important thing to do:

Get rid of mildew and/or mold right away. Second most important: prevent any future growth.

If you leave mildew or mold alone, both will continue to grow.

How to Get Rid of Mildew and Mold:

Our customer service team gets questions about mold and mildew, and we’d like to share some of their expert advice with you on how to get rid of mold and mildew and prevent it from taking hold of your hot tub.

Hand in pink glove wiping down hot tub surface with a yellow rag

If you spot mildew, clean it up immediately with a mild soap and dry the area.

If you spot mold, follow these steps to get rid of it:

  • Shock the hot tub and use a hot tub purge product to clean the pipes prior to draining
  • Drain the hot tub
  • Clean all surfaces of the hot tub with a mild detergent (it is important that any mold spores are cleaned off any porous surface).
  • If using bleach on your cover and/or pillows, check your manual to learn if it’s appropriate to help kill off any mold spores
  • Expose the hot tub and cover to sunlight; this will help kill mold spores as UV light acts as a natural oxidizer
  • Remove the plastic-wrapped foam panels from the vinyl cover. Clean with mild detergent or (if manufacturer recommends it) a diluted bleach solution. Allow to dry and inspect for torn plastic before reinstalling
  • Replace filter
  • A cover that has become waterlogged over time will not provide good insulation and will be more susceptible to mold. Contact your dealer to see when your cover should be replaced.
  • Drain your hot tub. Refill, and balance your hot tub water
A man crouched over the hot tub, holding a hose that is refilling the tub with water.

Prevention: the best defense against mold and mildew

  • Maintain water balance: regularly test Total Alkalinity, pH and Total Hardness to ensure they are in the correct levels
  • Ensure that your sanitizer is full and working properly
  • Clean the filter regularly, typically monthly
  • Using the hot tub regularly allows for humidity between the water line and cover to escape; if the hot tub is outside, regular use also exposes the cover to the sun’s UV rays, which helps kill mold spores
  • Use a hot tub purge product to clean the pipes in the hot tub prior to draining (typically every 3-4 months)
  • Regularly clean the surfaces; take a few minutes weekly or at least monthly to clean and dry surfaces, the cover and pillows and the area at the water line and above.
  • Use a manufacturer-approved conditioner / protectant on the spa cover and pillows
  • Consider FROG® products, then you can kill bacteria 2 ways, with a significantly low amount of chlorine or bromine and FROG Sanitizing Minerals

If you have further questions please contact us at 800-222-0169 or customer.service@kingtechnology.com, we’re happy to help.

We also have a chat box on our website for quick answers!

A few minutes to keep your hot tub, cover, pillows, surfaces, filter and pipes clean will prevent mold or mildew from taking hold.

Then, you can immerse yourself in the sheer bliss of your hot tub without a care. Ahhh…

An older gentleman reclining in the hot tub with his eyes closed.
  1. CDC.gov What are molds?

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