preventing mold growth hot tubs

In part one of this two-part blog series, we discussed the basics surrounding several mold types that can sometimes be found in or around hot tub areas. Mold, which requires moisture and enclosed spaces to grow, can be both unsightly and dangerous to human and animal health, meaning keeping it from forming anywhere on your property is important.

At Dolphin Pools & Spas, we’re a proud provider of Bullfrog Spas and many of their high-quality materials and products. In today’s part two, we’ll dig into one more mold type we didn’t get into in part one, plus some other basics on removing and preventing mold if it’s a concern near your spa or hot tub.

Pink Slime

Often accompanying white water mold, which we discussed in part one, is pink slime, or sometimes a pink sludge material. You can usually find this substance encasing the spa filter and above the water line, or potentially coating the plumbing within the tub itself.

In reality, pink slime is a form of bacteria that can build up in any moisture-heavy area. It can also sometimes be found in bathtubs, sinks and toilets. It’s resistant to chlorine and many sanitizer formats, and while it’s not harmful from a health standpoint, it looks disgusting and can be hard to get rid of. It’s often caused by poor water circulation, poorly-treated water or improper hose usage.


A related buildup that may show up in similar areas as mold is moss, but it’s important to note that moss is not harmful in the same ways as mold. It can often be found on the outside or top sections of spa covers, particularly those made from vinyl, as it grows in damp and shady conditions. It can be removed with a CleanAll solution and a basic scrubbing sponge.

Mold and Slime Removal

Some general steps for removing white mold and pink slime (black mold can be a bit tougher):

  • Lower tub pH balance to 7.2.
  • Remove and discard tub filter.
  • Shock the tub with at least eight teaspoons of Dichlor granules for every 250 gallons of spa water, then let the dose circulate for an hour.
  • Add four tablespoons per 250 gallons of Oxy-Spa solution, then circulate for another hour.
  • Add Spa System Flush to help clean plumbing areas, then run pump and jets for at least two hours.
  • If necessary, repeat the above steps to remove biofilm and remaining crud.
  • Empty the tub and clean the spa shell, footwell, jet faces and any other exposed pipes with CleanAll and a damp cloth.
  • Refill the tub, then add another high dose if dichlor. Allow for another two hours or more of circulation.
  • Add your normal sanitizer.

Sanitizer and Prevention

In many cases, however, mold of all types can be prevented through proper care and sanitizer use. Sanitizer destroys mold microbes before they can grow, but not all sanitizers are created equal. The CDC recommends a few top sanitizer options for disinfecting hot tubs:

  • Chlorine (necessary in virtually all sanitizers, per the EPA)
  • Bromine
  • Certain mineral sanitizers combined with an oxidizer

On the flip side, products like ozonators, UV and oxidizers (non-chlorine shockers) are not considered primary options. These can all help reduce chemicals, but should be used in coordination with proper sanitizers.

For more on preventing mold growth in or around your hot tub, or to learn about any of our new swimming pool or spa options, speak to the staff at Dolphin Pools & Spas today.