Hot tub algae manifests as green, yellow, or black growths clinging to surfaces or clouding the water. These growths are often single-celled organisms like Cyanobacteria. While the algae itself is rarely poisonous upon contact, its presence indicates a severe failure in the hot tub’s sanitation system. This failure creates an environment where harmful waterborne pathogens can thrive. Therefore, an algae-infested hot tub is unsafe, not because of the algae directly, but because of the dangerous microorganisms it signals and supports.
Health Risks Associated with Hot Tub Algae
The true danger of hot tub algae stems from the sanitation lapse that allowed it to grow. Low sanitizer levels enable the rapid proliferation of pathogenic bacteria like Pseudomonas aeruginosa. This bacterium causes hot tub folliculitis, or hot tub rash, which appears as itchy, red, pus-filled bumps around hair follicles. Symptoms usually appear within a few days of exposure to the contaminated water.
Legionella bacteria pose another serious respiratory threat, flourishing in warm, poorly maintained water systems. Inhaling aerosolized water droplets contaminated with Legionella can lead to respiratory illnesses such as Pontiac fever or the more severe Legionnaires’ disease. The warm temperatures and low sanitation indicated by algae create an ideal breeding ground for these organisms.
Algae actively undermines the water’s chemical balance. As it grows, the algae consumes the active sanitizer, such as chlorine or bromine, rendering the remaining chemical ineffective against other microorganisms. This consumption accelerates the depletion of the protective chemical barrier, allowing pathogens to multiply faster. Furthermore, the algal biofilm creates a slick, slimy surface on the tub’s shell and steps, introducing a physical hazard for slips and falls.
Factors Contributing to Algae Formation
Algae growth is a direct result of inadequate water maintenance. The primary factor allowing growth is a low or zero concentration of a chemical sanitizer, such as chlorine or bromine. Once the sanitizer level drops below the effective residual, algae spores entering the water from the environment, bather-introduced contaminants, or the air can begin to multiply without restriction.
The water’s pH level plays a major supporting role in this process. Chlorine, the most common sanitizer, becomes less effective when the pH rises above the ideal range of 7.2 to 7.8. A high pH can therefore mimic the effect of low sanitizer, allowing algae and bacteria to flourish even if sanitizer appears present on a test strip.
Warm water accelerates the growth and reproduction rates of algae once the chemical balance fails. Hot tubs left uncovered are exposed to sunlight, and the ultraviolet (UV) light acts as a fuel source for photosynthetic organisms like algae. The constant introduction of organic nutrients from sources like body oils, lotions, and dirt, combined with a dirty or clogged filter, provides a steady food supply for the algae.
Effective Algae Eradication and Prevention
Eradicating an existing algae problem requires aggressive chemical treatment, beginning with shocking the water. This involves adding a large dose of granular chlorine or non-chlorine shock to rapidly raise the sanitizer level, which is designed to overwhelm and kill the algae. For severe infestations, particularly deep-rooted black algae, the entire tub should be drained after shocking to ensure complete removal.
Once the water is drained, all surfaces, including the shell, jets, and filter housing, must be thoroughly scrubbed to remove any remaining biofilm and residue. The filter cartridges should be chemically cleaned or replaced entirely, as they can harbor spores and act as a source of reinfection. After cleaning, the tub should be refilled with fresh water, which must then be tested and balanced immediately, adjusting the total alkalinity and pH before any sanitizer is added.
Long-term prevention relies on a consistent maintenance routine to ensure the environment is hostile to growth. Water testing should be performed two to three times per week to monitor sanitizer and pH levels. Maintaining a proper sanitizer residual is paramount, as is routinely cleaning or replacing the filters to remove accumulated organic matter and trapped spores. Keeping the hot tub covered when not in use minimizes the entry of airborne spores and blocks the sunlight that fuels algal growth.