A sensory deprivation tank, often called a float tank or isolation tank, is a light and sound-proof environment containing a shallow pool of water. This specialized enclosure is designed to limit external stimuli, allowing the user to experience deep relaxation. The primary function of the tank is to create a sense of near-weightlessness, which is achieved entirely through the unique composition of the water solution inside.
The Necessary Salt Concentration
The quantity of salt utilized creates a solution far denser than normal seawater, making the floating experience possible. A standard float tank typically holds between 150 and 200 gallons of water. Approximately six pounds of salt are dissolved into every gallon of water to achieve the required buoyancy. This results in a total salt load between 900 and 1,200 pounds for a single tank, which elevates the water’s density to effortlessly support the human body.
The Specific Salt Used: Magnesium Sulfate
The salt used in sensory deprivation tanks is pharmaceutical-grade Epsom salt, chemically known as magnesium sulfate (\(\text{MgSO}_4\)), not common table salt (sodium chloride). This compound is chosen because it is non-toxic, highly soluble, and gentle on the skin and hair. The high solubility of magnesium sulfate allows for the creation of an extremely dense solution without causing the skin irritation associated with sodium chloride brine.
The Physics of Buoyancy and Density
The ability to float effortlessly is a matter of density. A typical human body has a specific gravity slightly greater than plain water, which is why most people sink or bob just below the surface. The addition of hundreds of pounds of dissolved magnesium sulfate significantly increases the overall mass of the water solution. This process elevates the solution’s specific gravity to approximately 1.27, making it heavier than the human body. The resulting environment creates neutral buoyancy, where the upward force exerted by the water perfectly counteracts the downward pull of gravity, allowing the muscles and skeletal system to relax.
Maintaining Water Purity in High-Salt Tanks
Even with the massive salt load, which naturally inhibits the growth of many pathogenic microorganisms, float tanks require a purification process. The salt solution is so concentrated—often reaching an 18% salt concentration—that it creates a hostile environment for bacteria, as organisms cannot survive in concentrations greater than 10% salt. This natural defense is supplemented by sophisticated filtration systems. The solution is circulated through a micron filter, which is fine enough to capture particulate matter, including shed skin cells and hair. This mechanical filtration is paired with sanitizers, such as ultraviolet (UV) light sterilization and hydrogen peroxide (\(\text{H}_2\text{O}_2\)), which destroy bacteria and viruses without leaving behind harsh chemical odors.