Survey of float tank operating practices

Float tanks are also known as sensory deprivation or isolations tanks and contain water with high concentrations of magnesium sulfate (MgSO₄) (Eykelbosha & Beaudet 2016). The high MgSO₄, or Epsom salt, solution concentration allows individuals to float on the liquid surface for experiencing restricted environmental stimulation therapy, which has been shown to improve physical and mental health (Kjellgren & Westman 2014; Eykelbosha & Beaudet 2016). Float tanks are currently reemerging in the United States since being introduced in the 1970s (Eykelbosha & Beaudet 2016). Two public health guidance documents on float tank operation exist in the US; the Model Aquatic Health Code (MAHC) and North American Float Tank Standards (Floatation Tank Association 2017; Centers for Disease Control & Prevention [CDC] 2018b). The extent of adoption and implementation of MAHC float tank language or the North American Float Tank Standard in the US is difficult to quantify. Therefore, documentation on standard operating practices within float tank facilities is lacking. Operation data are useful for understanding the spectrum of management practices in float facilities and how these practices differ from swimming pools and spas. Information about standard operating practices can also be useful for determining the need for regulation and auditing float tanks. The goal of this study was to gain an understanding of typical float tank operating practices by issuing a questionnaire on water treatment type and frequency, water chemistry testing and monitoring, user education and operator training.

A list of questions was generated considering common float tank operating practices that could be compared to swimming pool operating practices. Questions about water treatment type and frequency, water chemistry testing and monitoring, user education and operator training were included. An anonymous, 35 question electronic questionnaire was created using Qualtrics Software XM, copyright 2020. Respondents were not permitted to access the survey more than once but could enter information about multiple float tanks at a single facility. The questionnaire link was posted in spring, 2020 to an online forum with 2,800 members associated with the float tank industry. Results from the questionnaire were analyzed in fall, 2020 in Excel (Microsoft Version 16.42, 2020). Members of the float tank industry online forum were not necessarily float tank facility operators. Membership also consisted of float tank manufacturers, researchers, suppliers and clients.

Forty-five float tank operators from 23 states across the US completed the questionnaire. The low response rate (45/2,800) is likely a result of the employment diversity of members in the online forum where the questionnaire link was posted. Table 1 summarizes the basic characteristics of float tanks reported on the questionnaire. On average, float tanks have a smaller volume of water compared to commercial spas (typically >300 gallons), users float for about an hour and a half, and the amount of MgSO₄ in solution was within the range recommended in the MAHC and North American Float Tank Standards (both documents suggest a specific gravity range of 1.23–1.3). The maximum reported float time (480 min) is likely a result of questionnaire respondents allowing clients to string appointments together and extend their float experience.

When asked what type of filter is used to treat float tank water, most participants reported using a micron bag filter (49%, 22/45). Use of cartridge filters was another common response (27%, 12/45). Others reported filter brand names that were difficult to interpret so were not summarized in this paper. Only 27/45 participants responded to a question about filtration frequency. Two of the 27 reported continuous filtration and 25/27 reported filtering between each user, if not more frequently.

When asked what resources were used to learn about float tank operation, the most frequent response was online resources, including forums, websites and podcasts (40%, 18/45). Common online resources reported were the Facebook Float Collective, Float Tank Solutions, the Daily Solutions Podcast and the Art of the Float podcast. Other frequently reported resources were an apprenticeship (18%, 8/45), training from the manufacturer (18%, 8/45) and self-taught (4%, 2/45). Some participants reported accessing more than one training resource.

Results show a spectrum of operating practices across US float tank facilities and operational distinctions between float tanks and swimming pools/spas. Eleven different combinations of disinfectants or disinfection systems were reported by survey participants, including the use of bromine and/or chlorine. Chlorine and bromine are not currently registered by the United States Environmental Protection Agency (USEPA) for use in float tanks (CDC 2018a). Additionally, preliminary research by the National Sanitation Foundation (NSF) found MgSO₄ interferes with the accuracy of measuring free available chlorine and total chlorine in nondiluted float tank water by some test kits (Rehbein et al. 2015). Although chlorine is the most common primary disinfectant used to treat swimming pool and hot tub water, it is not appropriate for use in float tanks. If float tank operators are unable to accurately monitor chlorine concentrations in solution, amounts could be too high or low, posing a risk of chemical exposure to users or giving float tank operators a false sense of security. A residual disinfectant is necessary for maintaining water quality in swimming pools and hot tubs but is not necessary for planktonic microorganism disinfection in float tank solutions. Float tanks are intended for one or two users per session so contaminant loading by bathers is low (Floatation Tank Association 2017). Three turnovers (95% of the volume) of the float tank solution can be achieved between clients at float facilities. If 95% of float water is passing through a series of treatment techniques between float sessions, like UV, ozone and filtration, contaminant loading (pathogens, organic matter from bathers, etc.) of the float tank water should theoretically be at a safe level for the next client. NSF has published equipment standards for float tanks in NSF/ANSI/CAN 50–2021 (NSF/ANSI/CAN 50 2021). Float tank disinfection systems certified to NSF-50 must be able to achieve 3-log kill or inactivation of bacteria in the main vessel after completion of the manufacturer's cleaning cycle between users.

More research is needed exploring the contaminant removal efficiency of micron bag filters. Understanding the efficiency of each treatment technique at removing contaminants from float water will help make predictions about water quality. Research is also needed exploring float tank water quality before and after three turnovers to assess and validate treatment technique efficacy.

Current disinfectant recommendations for float tanks in the MAHC are ozone or UV only (CDC 2018b). Guidelines in the North American Float Tank Standards suggest use of hydrogen peroxide in conjunction with UV, ozone in conjunction with UV, ozone alone or UV alone (Floatation Tank Association 2017). Hydrogen peroxide is not a registered disinfectant by the USEPA and is used in float tanks to improve water clarity. At the concentrations used in float tanks hydrogen peroxide is not biocidal but rather functions as an oxidizer of organic matter. Anecdotal evidence suggests float tank operators using chlorine are instructed to by environmental health authorities. State or local health authorities creating regulations for float tank operation should be referring to existing guidance in the MAHC or North American Float Tank Standards to appropriately manage float solution disinfection. Anecdotal evidence from float tank operators also suggests MgSO₄ interferes with pH and alkalinity test kits. More research is needed exploring the accuracy of chemical testing kits designed for the swimming pool industry and used by float tank operators.

Study results indicate an interest in float tank operation guidance. The majority of participants sought educational resources on float tank operation (only 2/45 reported ‘self-taught’) and all facilities reported using a disinfectant, which suggests operators are motivated to maintain safe environments for patrons. Although float tank use poses minimal risk to patrons, licensing and inspection programs should be considered by environmental health authorities. Auditing float facility operation and maintenance would minimize the likelihood of impaired water quality and unsafe chemical storage and use. Pseudomonas aeruginosa cases associated with float tank use have been documented (Hyllestad et al. 2019; Rehbein et al. 2019). In one report, Rehbein and colleagues describe a single case of folliculitis from Pseudomonas that developed after an exposure to untreated float tank water. Staff at the float tank facility where the exposure occurred had unintentionally instructed the affected client to use a float tank that had been out of service for several weeks. No filtration or disinfection by UV or chlorine had occurred while the tank was out of service, and the specific gravity was not tested to verify the proper concentration of MgSO₄ was present. Five days after the exposure, local public health authorities collected water samples from the float tank. Results indicated the presence of Pseudomonas aeruginosa in the float tank water. Although the facility was licensed and inspected, this case study illustrates the potential for Pseudomonas growth in float tanks if the MgSO₄ concentration, disinfection and filtration are not properly maintained that may result in human health risks. In another report, Hyllestad et al. (2019) describe 22 cases of illness ranging from rash to ear canal pain from Pseudomonas aeruginosa exposure in an art installation intended to mimic the sensory deprivation experience. The basin was built in the 1990s and displayed and maintained by museum staff at an art gallery in 2017 as part of an exhibition open for 18 days. Art exhibition staff were responsible for maintaining and monitoring MgSO₄ and chlorine (which cannot be accurately measured in high MgSO₄ solutions) in the basin based on advice from a consultant. At the time of the site investigation by public health authorities, the chlorine concentration ranged from 0.01 to 0.02 mg/L, which was below local guidelines for pools. No local guidance existed for free available chlorine concentrations in saline water, like float tanks. Only two documented chlorine concentration measurements could be presented during the site visit. An MgSO₄ monitoring device was installed but was not in use during operation. Water samples collected by public health authorities were positive for Pseudomonas aeruginosa in ‘massive’ quantities. Since the art exhibition was meant to mimic the floating experience, this case study does not reflect the best management practices occurring at commercial float facilities. However, it does illustrate potential risks associated with recreational water quality mismanagement.

The resulting cases of Pseudomonas infection from float tank/basin use at these facilities provide evidential support for float tank regulation since each case illustrates the possibility of pathogen transmission. Although the facility described by Rehbein et al. (2019) was licensed and inspected, health authorities cannot be present to oversee operations at all times. Licensing ensures all facilities are held to the same cleanliness and operating standards and minimizes the risk of imminent health hazards, but negligence and poor operation of float facilities poses a danger to public health regardless of regulation and inspection. Closure signage on nonoperational float tanks is a best management practice and could have prevented the Pseudomonas case described by Rehbein et al. (2019). Education during an opening and follow-up inspection after licensure by health authorities could have prevented the outbreak described by Hyllestad et al. (2019). Most public venues that pose some risk to human health are licensed and inspected in the US by environmental health practitioners. Venue examples include massage parlors, tanning salons, body art facilities, temporary food stands, restaurants and swimming pools. Although float tanks may pose a lower risk to users than swimming pools, they still pose some risk. The risk of infection from fecal-oral pathogens, even in poorly maintained float tanks, is likely lower than swimming pools because float tank users avoid mouth-contact with the saline water (Floatation Tank Association 2017) and therefore water ingestion. The risk of skin infection from organisms like Pseudomonas aeruginosa appears to be lower in float tanks than pools based on reported outbreaks. Only one outbreak and one illness case associated with a float tank and a basin mimicking a float tank have been published since the 1970s (Hyllestad et al. 2019; Rehbein et al. 2019). In just one year (2011–2012), there were two confirmed and four suspected outbreaks of Pseudomonas aeruginosa in US-treated recreational water venues, like swimming pools (Hlavsa et al. 2015). Over the course of 14 years (2000–2014), 47 outbreaks of Pseudomonas aeruginosa in treated recreational water venues were reported in the US (Hlavsa et al. 2018). Facility inspections by public health authorities identify and prevent problematic management practices that can lead to adverse health effects like those described by Hyllestad et al. (2019) and Rehbein et al. (2019). Inspections also provide an opportunity for health authorities to educate operators on appropriate management practices according to local health and safety regulations.

Although chlorine is the most common primary disinfectant used to treat swimming pool water, it is not appropriate for use in float tanks because concentrations cannot be accurately monitored. More research is needed exploring chlorine, pH and alkalinity test kit accuracy in water with MgSO_4. Additionally, more research is needed exploring water treatment efficacy of micron bag filters, which are commonly used in float tanks.

Most public venues, except for most float tanks, that pose some risk to human health are licensed and inspected in the US by environmental health practitioners. Although float tanks pose a lower risk to users than swimming pools, they still pose some risk and health authorities should consider licensing and auditing float tank facilities. Additionally, state or local health authorities creating regulations for float tank operation should use existing guidance in the MAHC or North American Float Tank Standards. Facility inspections identify and prevent problematic management practices and provide an opportunity for operator education.

Data cannot be made publicly available; readers should contact the corresponding author for details.

Ashkahn Jahromi owns a float tank facility. His expertise on float tank operation was necessary to appropriately develop the questionnaire on float tank operations.