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Epsom salt has uses ranging from personal care to large-scale agriculture, and, of course, it is the salt that brings the ‘float’ to float tanks. Since it plays such a key role in our industry, and in maintaining the chemical balance of our beloved float tanks, we wanted to shed some light on the grading system of Epsom salt.

Because of the wide scope of uses, only some of which require and expect the most pure Epsom salt, a grading system has been established so that customers know what to expect in regards to salt quality and purity.

Since float tanks take about 700-1000 lbs of Epsom Salt each, maintaining float tanks means becoming familiar with the different classifications of the salt, to make sure you’re getting exactly what you need.

Grading System

One of the first things you’ll need to do is decide what grade of salt to purchase. A lot of Epsom salt, especially imported salts (because they are subject to different rules and regulations), use varying combinations of terms to describe the quality of their salt. Despite these many terms you may hear used to describe the quality, there are only two distinct ‘grades’ of Epsom salt:

  1. USP Gradewhich stands for United States Pharmaceutical Grade, and is often also referred to as Food Grade. This is the most quality controlled Epsom Salt, expected by the manufacturer to be used in personal care products and food. Because of these uses, which require a more consistently pure salt, each batch of USP grade is tested and the quality of the salt is guaranteed.
  2. Technical Grade – also known as Agricultural Grade or Industrial Grade, and is produced by manufacturers for use in these environments. The uses of Epsom salt on an industrial or mass-agricultural level do not require that the Epsom salt be as pure as USP grade salt. Because of this, manufacturers test these batches of salts less regularly, and there is a chance that certain batches contain impurities.

You could also say there is a third ‘grade’ of salt, which is Asian epsom salt. The only manufacturers of USP grade Epsom Salt are The PQ Corp (US based), Giles (US based), and K+S (Germany based). Salt from Asia (China and India, primarily) is almost always cheaper, however, it is more unregulated, and through personal experience we’ve found that heavy metals and impurities in the salt can cause unfortunate float tank interactions (such as your float solution turning dark brown).


Which grade of Epsom salt should be used in float tanks?

Interestingly enough, despite there being two distinct grades of Epsom salt, there is very little different about the salt itself. Technical grade and USP grade are made in the same plants, on the same machines, from the same materials.

The only difference between two is that USP grade has been certified by the FDA, whereas Technical grade has not. This certification requires that every batch of USP salt be tested for impurities, while only a fraction of the batches of technical grade are tested.

In all likelihood you would get the exact same salt, no matter which you ordered, as long as it’s from one of the three main manufacturers. However, because not every batch is tested, it’s also possible for extra heavy metals and other impurities to be present in technical grade salt, whereas purity is guaranteed with USP salt.

Because of the guaranteed quality, we recommend USP grade for use in float tanks. While technical grade is definitely cheaper, it may contain impurities such as iron, manganese, and other metals. Impurities in the salt can upset the chemical balance of the float tank, cause the water to brown, and even cause damage to your pump if build-up occurs. If you know the quality of your salt from the start, you can eliminate it as a potential cause to any float tank mishap which might occur, saving you valuable time in locating the source of the problem at hand.

For more information, on the Epsom salt grading system, check out this great presentation given by Dan Elmer at the 2012 Portland Float Conference. Dan Elmer is one of the owners of the San Francisco Bath Salt Company.


As always, if you have any questions or comments about epsom salt, or any questions about floating in general, feel free to contact us!

Frank Ciavarello, Float Tank Solutions