Swimming in a slimy pool is not safe. The slick, unpleasant feeling is a direct warning sign that the pool’s water quality has failed, allowing microbial life to flourish. This contamination indicates the presence of a protective layer of microorganisms that can harbor harmful pathogens. When the water is no longer properly sanitized, the risk of contracting various waterborne illnesses significantly increases.
What Causes Sliminess in Pool Water
The sliminess felt in pool water is primarily caused by biofilm, a complex matrix of microorganisms. Biofilm forms when bacteria, algae, and other microbes adhere to a surface and encase themselves in a protective, self-produced slime layer called an Extracellular Polymeric Substance (EPS). This coating shields the microbes from chemical sanitizers, allowing them to multiply unchecked on pool surfaces and inside the filtration system.
The growth of this slick layer is fueled by the pool’s organic load, which includes materials like sweat, body oils, sunscreen, and dirt introduced by swimmers. These contaminants serve as a nutrient source, accelerating colonization and biofilm formation. Slimy water signals that the disinfection system has been overwhelmed by this organic matter.
Algae growth, such as green or yellow algae, is often a visible component of this sliminess and indicates a sanitation problem. When algae settle on surfaces and combine with bacteria, they contribute to the slick, sticky texture characteristic of established biofilm.
Health Risks of Swimming in Contaminated Water
Swimming in slimy water exposes individuals to a high risk of contracting Recreational Water Illnesses (RWIs). These illnesses are caused by ingesting, breathing in mists of, or having contact with water contaminated by various pathogens harbored within the biofilm.
The most common RWIs are diarrheal illnesses caused by germs like Cryptosporidium (Crypto), Giardia, E. coli, and norovirus. Cryptosporidium is particularly concerning because it is highly resistant to standard chlorine levels and can survive in treated pool water for several days. Swallowing contaminated water can lead to symptoms like vomiting, stomach cramps, fever, and persistent diarrhea.
Contaminated pool water can also cause other infections. Skin rashes, such as folliculitis caused by the bacterium Pseudomonas, are common when the disinfectant is inadequate. Swimmer’s ear, a painful outer ear infection, and eye irritations are frequently linked to water where microbial growth has gone unchecked.
How Pool Chemistry Failures Lead to Biofilm
The development of a slimy pool is a direct consequence of failing to maintain the proper chemical balance, which is the pool’s primary defense system. The most common failure involves inadequate sanitizer levels, typically chlorine or bromine, necessary to kill bacteria and prevent microbial colonies. When the sanitizer level drops too low, microbes are free to colonize surfaces and initiate biofilm formation.
A second failure is improper pH balance, which directly affects the sanitizer’s effectiveness. Chlorine is most efficient at a pH between 7.2 and 7.4. If the pH rises above this range, the chlorine becomes chemically less active. This renders the sanitizer largely ineffective, allowing microbes to proliferate and establish biofilm.
Furthermore, the continuous breakdown of organic contaminants consumes the existing sanitizer, known as high sanitizer demand. This consumption rapidly depletes the pool’s free chlorine, preventing it from tackling new microbial threats.
Safely Restoring a Slimy Pool
Restoring a slimy pool requires both mechanical removal and aggressive chemical treatment. The first step is to mechanically disrupt the biofilm by thoroughly brushing all pool surfaces, including the walls, floor, and steps. Brushing breaks the protective EPS layer, exposing the underlying microbes to the sanitizer.
After brushing, the water must be subjected to shocking or super-chlorination, which involves adding a high dose of chlorine to rapidly destroy the remaining organisms. This high concentration is necessary to eliminate pathogens and overcome residual biofilm. Following this treatment, the pool’s filtration system must run continuously to circulate the water and remove dead organic matter.
The pool should not be used for swimming until the water is completely clear and the chemical balance is verified. The free chlorine residual must return to a safe level, and the pH must be adjusted back into the ideal range of 7.2 to 7.4. Consistent testing is mandatory to ensure the water is safe.