Pink Slime (and its “buddy” White water mold) is a newer problem facing swimming pool owners over the past 10 – 20 years. They are naturally occurring and are caused only by a lack of proper pool maintenance and water chemistry. In fact, even non-pool owners struggle with the pink slime in bathrooms, kitchens, and washrooms. Ever notice that pink ring around the basin? That’s pink slime.

Let’s define what pink slime is. Pink slime is a naturally occurring bacterium (of the newly formed genus Methylobacterium). Pink Lime is NOT a form of Algae, it is animal not vegetable. It is pink- or red-pigmented and forms a heavy, protective slime coating which provides the organism with an unusually high level of protection. Pink slime consumes methanol (a waste gas) and it is oftentimes found WITH White Water Mold. This organism is very resilient and resistant against halogen-based (chlorine or bromine) as well as non-halogen sanitizers or germicides and can remain a contaminant even after treatment.

Although initially found in swimming pools being treated with biguanides (Baquacil, Soft Swim, Polyclear, etc.), it is now seen in any and all swimming pool environments. This is NOT a biguanide problem ONLY nor is it CAUSED by the use of biguanides.

The pink slime bacterium has an affinity for the matrix that exists on the surface of PVC plastics; it will attach itself to & inside of the matrix, allowing it to re-contaminate long after it appears that it has been seemingly “destroyed” (includes pool toys, floats, ladders, steps, fountains, automatic pool cleaner parts, skimmer baskets, weirs, directional fittings, garden hoses, etc.). Small quantities of pink slime can lead to a re-establishment of the problem. It is caused by improper water & pool maintenance, environmental factors and poor circulation. Pink slime prefers areas that are “dark” (not exposed to direct sunlight) & with “slow moving” water. In another industry, medical technology, this bacterium occurs regularly in laboratory tubin.

Look for pink slime under ladder treads, behind the skimmer weir, on the undersides skimmer baskets, pool directional returns, underwater pool light niches and light housings. If you find that the pool just isn’t holding chlorine, bromine, or even hydrogen peroxide used in biguanide treated pools, look for pink slime.

After regular tracking of homeowners swimming pools affected by pink slime, here are some commonalities:

  • Many, but not all, affected pools have “smaller (under) sized” cartridge filters. (i.e. using a 75 sq ft filter on a 24 ft Rnd aboveground pool or a 90 sq ft filter on a 15 x 30 inground pool).
  • Affected pools get 6 hours or less of direct sunlight on the pool surfaces.
  • Pool owners always leave the solar blanket on AND don’t chemically clean the blanket the recommended 2 times per year to remove the accumulated biofilm.
  • “Shocking” or oxidizing of the pool water is not done with the recommended label instructions. For example, rather than shocking the pool every week or two, that task is neglected because the water “looks fine.”
  • Rainy pool seasons see a dramatic rise in the cases of pink slime.
  • Customers regularly add fresh water from their tap without letting the hose-water run for a couple of minutes (the pink slime is already present in the garden hose and is transferred to the pool).
  • Pools with sand filters are not changing the sand every 2 to 3 years AND not chemically cleaning the filter sand 3 times a season (once every 6 to 8 weeks).
  • Newer observation: Most of the affected seem to use publicly treated drinking water. Pools filled with well water appear to be not as severely affected.
  • Affected pools are not as fastidiously maintained chemically (water balance, use of borate additives such as BioGuard Optimizer Plus or Proteam Supreme, regular shocking), as clean pools.

Another observation is that many water companies across the country, in partial response to “consumer calls” to “get rid of chlorine in the drinking water” are now using mono-chloramines to treat the water (over the past 15 to 20 years). Mono-chloramines do an essentially good job at treating pathogens in the drinking water, however, some of the non-pathogenic organisms may indeed be getting by. Unfortunately, there is only experiential or anecdotal evidence.

Prevention of “pink slime” is preferred over treatment. Follow these steps to help prevent pink slime:

  1. Physically brush & clean ALL Pool surfaces weekly, including ladder steps (especially underneath each step) & rails
  2. Expose ALL pool surfaces to as much sunlight as possible (sunlight & UV are natural oxidizers)
  3. Remove the lid from the skimmer to allow sunlight into the basket for several hours each day ** INGROUND POOLS 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. Regularly add oxidizing chemicals into the skimmer to purge & clean the filtration lines of any bio-film (use extreme caution if doing this. Add chemicals slowly and remove ANY and ALL objects, including slow dissolving chlorine tablets or sticks, to avoid a potential chemical reaction such as explosion.
  5. 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 pool.
  6. Regularly clean pool toys & floats (use BioGuard Stow Away acting as a mildewcide)
  7. Regularly clean pool solar blanket (use BioGuard Stow Away)
  8. Chemically clean the pool filter every 4 to 6 weeks (use Strip Kwik, Kleen It or Soft Swim® Filter Cleaner). This is a very important step regardless of the filter type; sand, DE or Cartridge.
  9. Add regular Maintenance dosages of “Shock” & Algicide every 1 to 2 weeks as prescribed (3 to 4 weeks in bguanide pools).
  10. Use borate products such as BioGuard Optimizer Plus as a preventative measure (borates, when used properly at a rate of 50 – 80 ppm, allow the sanitizer to sanitize rather than sanitize and prevent algae growth).
  11. Run the filter a minimum of 12 hours daily to prevent “dead spots” in the pool.
  12. Remember to clean & rinse the brushes, hoses & vacuums that you use to clean the pool
  13. Leave as much of your pool equipment exposed to the sun (sunlight is a natural oxidizer)
  14. Keep the water balanced at all times. Recheck after heavy usage or rain or large “top-offs” of new water. Water balance refers to Free Available Sanitizer level, pH, Total Alkalinity, Calcium Hardness.

Treatment of “pink slime” MUST BE QUICK AND TOTAL! DON’T SKIMP!

Clean all pool & affected surfaces as prescribed above.

Physically clean & remove all visible “pink slime”

Add an initial dosage of algicide to the pool

“Shock” the pool with a triple or quadruple dose

Run filter 24 hours daily until water is clear & halogen or peroxide levels are maintained at a “higher” level

Chemically clean the filter. Simple rinsing or backwashing of the filter will not remove the greases, oils & other accumulated contaminant from the filter and filter tank.

Have the pool water professionally tested & analyzed. Look for a pool company that knows what they are talking about and isn’t afraid to tell you the truth about problem.

Maintain Optimizer Plus (or other borate product) levels

Maintain good water balance of pH, Total Alkalinity & Calcium Hardness

The longer that you allow the pink slime to remain, the more difficult it will be to cure.


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