Water Conditioning & Purification Magazine

Eliminating Mold & Slime in Swimming Pools

By David Rouse

Summary: As we head into the throes of summer, many of us are looking forward to using the backyard swimming pool. Very few of us, however, will think about what’s in that water and whether or not it’s safe. This article tries to shed some light on the topic.


For years, the only way to maintain perfectly balanced swimming pool water was with traditional chlorine treatment programs. Now, there’s an alternative swimming pool water treatment designed to increase the enjoyment of those pool users who are sensitive to the traditional chlorine maintenance programs or just want something different. Using biguanide (poly-hexamethylene biguanide, or PHMB) makes swimming pool water feel soft to the skin, eyes and hair while effectively sanitizing pool water and killing bacteria. Until recently, this alternative treatment also came with a less than desirable side effect—pink slime and white water mold.

This article will define pink slime and white water mold, how to kill them once they emerge and, finally, how to prevent them.

Pink slime, white mold
Pink slime and white water mold grow in the hard-to-reach plumbing and filtration systems of poorly circulated swimming pools. They’re characterized by stringy pink growths or cloudy white tissue paper-like growths behind ladders, inside skimmer baskets, plumbing and filtration systems.

Pink slime is a mixture of bacteria and other microorganisms which can also appear cloudy or whitish in color. These bacteria can live in colonies that may be composed of the same or several species, which makes classification very difficult. Pink slime clings and grows on a wide variety of surfaces with ease and exhibits the tendency to form layers, in which one layer can grow on top of another. Each layer has its own protective coating that can feel slimy to the touch. Furthermore, pink slime may be transmitted through air, soil, dust, and numerous other substances, and is present in fresh water systems throughout the United States.

On the other hand, white water mold is fungal by nature with a fuzzy, powdery, wooly or velvety and an occasionally smooth texture or characteristic. Color may range from white to shades of pink, violet, yellow or gray tones. It should be noted that mold, unlike bacteria, is a common airborne fungus found naturally in the environment.

Pink slime and white water mold may develop in biguanide-treated swimming pools for the following reasons:

  • Low levels of biguanide and/or hydrogen peroxide,
  • Poor circulation and flow, which allow pink slime and white water mold to adhere and multiply, and
  • Lack of proper swimming pool maintenance including filter neglect and failure to provide adequate cleaning by using a brush to clean surfaces (corners, seams, PVC tubing, etc.).

Modern method
What do you do to get rid of pink slime and white water mold once you have it? There are two ways to eliminate pink slime and water mold in biguanide treated swimming pools. The easiest and most modern method uses tablets that form chlorine dioxide when added to water to penetrate into the plumbing system to kill the slime and mold harbored in the circulation system. Chlorine dioxide is a powerful oxidizer commonly used in wastewater and drinking water treatment. Chlorine dioxide gas is yellow and heavier than water, which allows it to seep throughout the entire plumbing system including the main drain line. If this solution isn’t available, then try the conventional closed-loop system as follows.

Conventional method
If the filtration, circulation and water balance have been checked, and the pool water is still cloudy or milky, check the closed-loop system. First, turn off the pump. Use a vacuum attachment and hose to create a connection from return fitting to a skimmer. Close off all other returns. Remove any products or trash from skimmer basket(s). Next, start the pump and slowly pour chlorinating solution into the skimmer where the vacuum hose will be attached. Lower the vacuum cover over the skimmer. This creates a closed loop from the skimmer to the return line and back through the skimmer. Allow circulation for 10 minutes, then turn off the pump, remove the vacuum attachment from inside the skimmer and place outside the pool. Restart the pump and allow water to flow from the end of the hose and away to waste. It’s important to make sure chlorinated water doesn’t mix with pool water. Biguanide and chlorine aren’t compatible. If they mix, the chlorine will react with the biguanide causing the pool to turn a cloudy greenish hue. Allow the pump to run for five minutes while it pumps water out of the hose. Repeat this process for each return fitting.

The program approach
Now that we’ve addressed what pink slime and white water mold are and how to kill them, the next question is how to prevent them?

It’s important to recall the soft, non-irritating features of the biguanide treatment. The best approach isn’t a one-time remedy but rather a biguanide-based swimming pool water maintenance program. Using a program approach assures constant quality of the swimming pool water, and the right program is simple to use and won’t take a lot of time.

Prevention of mold and slime
The best solution currently available to combat pink slime and white water mold in biguanide-treated swimming pool water is based on an easy-to-use ABC program. The A step of the three-step program should include a highly effective quaternary ammonium algaecide with a high concentration of C14, one that works to prevent algae growth before it starts. As temperatures increase, algaecide becomes more important in preventing algae bloom. The B step employs a U.S. Environmental Protection Agency (USEPA) registered solution (PHMB) that sanitizes pool water and controls bacteria when the level of the solution is maintained between 30 and 50 parts per million (ppm). In many pools, applications are only required every two weeks. The C phase of this program must involve an enhanced hydrogen peroxide product that keeps water clear by removing contaminants that cause cloudiness.

Using the ABC program will make swimming pool water soft and brilliant. To prevent pink slime or water mold, however, add a maintenance application of chlorine dioxide once every three to four weeks. This maintenance dose of chlorine dioxide prevents the excessive consumption of the hydrogen peroxide that’s symptomatic of slime and mold in the system. This translates into savings in terms of the user’s time and money.

Does it work for everyone?
The biguanide program discussed in this article is ideal for residential pools up to 25,000 gallons. Well-circulated swimming pool water in pools with sand filters are the best candidates for this type of program. The program is effective on any surface type, but performs exceptionally well with vinyl-surfaced swimming pools.

This type of program is great for pool owners who are good about following directions, prefer an alternative to chlorine, new to owning and maintaining a swimming pool, or want an easy-to-follow program.

Conclusion
Regardless of which of these categories fits a particular situation, having soft, gentle swimming pool water without worrying about pink slime and white water mold is something every pool owner should expect. The information presented in this article will allow swimming pool owners to properly maintain a biguanide-treated swimming pool. Rest assured, using this method will add life and enhanced performance to equipment for clear, soft and perfect pool water.

About the author
David Rouse is manager of technical services for BioGuard Inc. and BioLab® Inc. With headquarters in Lawrenceville, Ga., BioGuard is one of the world’s largest manufacturers of pool and spa chemicals. The company’s line of biguanide swimming pool and spa products includes the SoftSwim® pool care program as well as the proprietary technology of SoftSwim Assist®, which is made with Aseptrol, a product of Engelhard Corp. Assist is a 100-gram tablet that contains sodium chlorite and dischlorisocyanurate dihydrate. When added to water, the sodium chlorite converts to chlorine dioxide gas. BioGuard retailers offer swimming pool and spa sanitizers, oxidizers, balancers, algaecides, winterizers and other specialty products for residential, service and commercial markets. Rouse can be reached at website: www.bioguard.com

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