Float tanks have been around since flotation REST (reduced environmental stimuli therapy) was developed in the 1950s by John C. Lilly, M.D. Also known as sensory deprivation tanks or isolation tanks, this therapy uses a water-filled tank that is approximately the size of a bed and is heated to skin temperature. The therapeutic benefits are many, not just because of the tank itself but also because of what’s in the water.

The idea behind float tanks is very simple. Patients don a bathing suit or other appropriate attire and then enter a pod-like, water-filled tank. The water in the tank is heated to skin temperature, around 91 degrees, so that the water is barely noticeable on the skin. This allows the patient to relax fully without the sensory stimulation of something touching their skin.

In addition to the light touch of the water, the room in which the float tank is located is dimly lit, and some patients may wear eye masks to further block the light. The resulting sensation is that of being in a cocoon, or even of returning to a womb-like environment.

What’s in the water?

The water in a float tank is a crucial part of the therapy. Float tanks include Epsom salts (magnesium sulfate) in near-saturation amounts, usually with a relative density of 1.25. Lilly initially recommended aiming for a relative density of 1.3, but at this level recrystallization is possible. A relative density of 1.25 is the same as the level of salt in the Dead Sea.

The goal for this amount of magnesium sulfate is twofold:

  • Floatation: One of the goals of float tanks is for the patient to be able to fully relax and let go of all effort. The high relative density of the float tank completely supports a patient and allows them to easily keep their mouth and nose above the surface with zero muscular effort. Initially it may be difficult for patients to let go fully, but as they spend more time in the tank, they will begin to see that they can truly relax and be supported by the water.
  • Therapeutics: People in the U.S. are chronically magnesium deficient. Magnesium sulfate is an often-ignored mineral that contributes to over 300 different functions in the body, including maintaining heart health. Many symptoms of magnesium deficiency are similar to chronic pain symptoms and can include muscle aches, insomnia, migraines, chronic fatigue, and fibromyalgia. Transdermal (across the skin) magnesium therapy is an excellent way to address these symptoms. Many people take Epsom salts baths to relax and unwind tired muscles. Float tanks offer the opportunity to do the same thing with the added benefit of complete muscle relaxation at the same time.

While the ability to float and relax is an important part of float tank therapy, the magnesium is arguably the most important part of the treatment. Because magnesium is so crucial to the functioning of the entire body, low levels of this mineral can lead to serious, systemic issues, including:

  • Type 2 diabetes: Researchers looked at 13 cohort studies with 536,318 participants reporting 24,516 cases of diabetes and found a significant inverse association between magnesium levels and Type 2 diabetes. In other words, where magnesium intake was up, incidence of Type 2 diabetes went down.
  • Cardiovascular disease: In a similar meta-analysis of 16 studies and 313,041 individuals, researchers found that magnesium intake was also inversely associated with the risk of cardiovascular disease. Low magnesium is also the number one predictor of heart disease, even above cholesterol and saturated fat intake.
  • Stroke: The results of seven studies with 241,378 participants and 6,477 cases of stroke found that an increase in magnesium brought about a small but statistically significant decrease in the risk of stroke.
  • Cancer: In eight studies, increased magnesium helped bring about a modest decrease in the risk of colon cancer, but other