Here’s what it is & what it looks like:
a naturally occurring fungus (NOT Algae; it is animal not vegetable)
white mucous or tissue paper-looking substance that forms on the inside surfaces of spas
forms a heavy, protective coating providing the organism with an unusually high level of protection that is very resilient & resistant against halogen-based (chlorine, bromine) & non-halogen sanitizers or germicides
white mold can remain a contaminant even after treatment
water mold thrives on the surface of PVC plastics including pipes & plumbing lines & air bubbler/blower lines
water mold is able to re-contaminate long after you believe that it has been destroyed (includes spa toys, floats, steps, fountains, filter interiors, filter cartridges, skimmer baskets, weirs, directional fittings, garden hoses, etc.)
small quantities can lead to a re-establishment of the problem
caused by improper water & hot tub maintenance, environment, poor circulation
prefers areas that are "dark" (not exposed to direct sunlight) & with "slow moving" water

Prevention:
Prevention of "white spa mold" is preferred over treatment. Follow these steps to help prevent white water mold:
1. Physically wipe & clean ALL spa & hot tub surfaces weekly, including recesses around all jets & underneath pillows
2. Expose ALL spa surfaces to as much sunlight as possible (sunlight & UV are natural oxidizers)
3. Remove the lid from the skimmer (if equipped) to allow sunlight into the basket for several hours each day ** INGROUND SPAS MUST USE EXTREME CAUTION in doing this in order to avoid a person falling into or otherwise injuring themselves due to an open skimmer.
4. When the water is changed use Spa System Flush or Whirlpool Rinse to break-up the build-up of bio-film in the pipes.
5. Regularly use SpaBoss Descummer to “eat up” unfilterables.
6. Regularly add oxidizing chemicals into the skimmer to purge & clean the filtration lines of any bio-film*
7. When adding make-up water from the garden hose, allow the water to run for 2 to 3 minutes before putting the hose into the spa. Due to the use of chloramines, you are finding more & more water mold & pink slime in almost ANY damp area.
8. Regularly clean spa toys & floats
9. Regularly clean spa solar blanket and/or the underside of your cover
10. Chemically clean pool filter every 4 to 6 weeks (use SpaBoss Filter Cleaner)
11. Add regular Maintenance dosages of "Shock" (SpaBoss Spa Shock or SpaBoss Chlor-Aid) weekly as prescribed
12. Run the filter a minimum of 6 hours daily to prevent "dead spots" in the water’s circulation
13. Remember to clean & rinse the brushes, hoses & vacuums that you use to clean your spa
14. Keep the water balanced at all times. Recheck after heavy usage or rain or large "top-offs" of new water. Test the water at least 2 to 3 times per week.  Water balance refers to Free Available Sanitizer level, pH, Total Alkalinity, Calcium Hardness.

Treatment:
Treatment of "white water mold" MUST BE QUICK AND TOTAL! DON'T SKIMP!
1. Clean all hot tub & affected surfaces as prescribed above.
2. Physically clean & remove all visible "white water mold"
3. "Shock" the pool with a triple or quadruple dose*
5. Run filter 24 hours daily until water is clear & chlorine or bromine levels are maintained at a "higher" level*
6. Chemically clean the filter
7. Maintain good water balance of pH, Total Alkalinity & Calcium Hardness

This information is used by permission.