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I’m happy to announce to first results from the Float Fund testing. This experiment, run through the NSF, was to see how salt water, with no other form of disinfection, actually effected harmful organisms. We ran tests with two different microorganisms, and in this post we’ll talk about how one (Pseudomonas) got its ass kicked by salt-water and how the other one (Enterococcus) didn’t seem phased in the slightest.

If you want to skip straight to the test results, you can download them in their entirety below. Since they have a lot of fancy laboratory lingo, we’ll spend the rest of this post breaking down the different aspects of the testing.

download pdfDownload the Full
MgSO4 Shaker Table Test Results

Why were these tests run?

This test is the first in a line of tests that we want to conduct to find out more about water sanitation in the float tanks. As an end result of our experiments, we would like to have strong evidence pointing to the efficacy of certain preferred disinfection options such as H2O2 + UV, and Ozone.

Before we launched into testing with disinfectants, however, we wanted to establish a baseline of how bacteria react with our float tank solution by itself. There is no chance of using only the Magnesium Sulfate for proper disinfection, but getting a baseline performance with only the salt water can give us information that is valuable for designing our later testing (such as what organisms are either damaged or unaffected by the float tank solution).

Designing the Experiment

We didn’t want to get too complicated with our experimental design, mainly because costs can go up very fast with this sort of thing. We decided to test only 2 organisms, taking 3 samples over a 24 hour period, both in saturated magnesium sulfate solution, and in regular water.

  • Enterococcus and Pseudomonaslab_pitri
    Enterococcus Faecium and Pseudomonas Aeruginosa are the two main bacteria on the NSF 50 Annex H (which specifies instructions for disinfection testing in recreational water).  Pseudomonas is common in recreational water (it is affectionately referred to as ‘Hot Tub Rash’). Enterococcus is an especially resilient organism. It is, as Rich Martin with the NSF put it, “like Apollo Creed from Rocky.”
  • Regular Water vs Salt Water
    To make sure we had a control group to compare results against, we ran the exact same series of experiments on both regular water and saturated Epsom salt solution.
  • Water samples taken at the start, at 1 hour, and at 24 hours
    The theory here was that we wanted to see if our float tank solution could actually significantly reduce bacteria after just a short time (the 1 hour mark). We also wanted to see what potential long term exposure to our salt water would do to our two organisms (24 hours).
  • Shaking every hour for the first 12 hours.
    We wanted to mix up the water regularly to simulate a regular pump cycle in a float center, and to break up bacterial colonies as they start to form, so the water was shaken for 15 minutes of every hour for the first 12 hours. We then allowed a 12 hour period of stagnation to simulate a float tank lying dormant overnight. We did one last shake at the 24 hour mark before taking the final water sample.
  • The only similar testing we know of was done by Float Lab (a float tank manufacturer in California), and in those tests the water was stagnant for the full 24 hours. Because of this, the shaking is one of the factors that we were especially curious about.
  • Replication: 3 Water Samples per Conditionlab_vial
    We had 3 water samples per condition, for a total of 12 (3 samples of regular water w/ both types of bacteria, and 3 types of salt water w/ both bacteria). The multiple samples then had their results averaged for more consistent results.

The Results

Organism Viability

This graph sums up the results pretty well, once you know what everything means – let’s dig in and see what’s going on here.


Let’s start by looking just at the first part of the graph. Along the left, we’re measuring the concentration of bacteria: the taller the bar, the more bacteria there are. The Ef control label at the bottom is saying that this is Enterococcus (as opposed to Pa for Pseudomonas), and fresh water (as opposed to epsom salt solution). The different color bars are for different time points: white is right when the test starts, light grey is an hour in, and dark grey is after 24 hours. You can see that for Enterococcus in fresh water, there was very little drop in bacterial levels over a 24 hour period.


Expanding this to include Ef Salt Water (or Enterococcus, in salt water) you can see that the results were pretty much the same. The extra salt seemed to have no effect on levels of Enterococcus.

Now, let’s look at Pseudomonas in regular water (Pa Control):


You can see that the levels of Pseudomonas rose over time, both at the 1 hour sampling point and at the 24 hour sampling point.

Finally, let’s see Pseudomonas in Epsom Salt Solution (Pa Salt Water) compared to the control:


Here you can see a dramatic difference. Pseudomonas, shaken over 24 hours in salt water, doesn’t fare well at all. In fact, the last (darker) bar on there is not quite accurate. That’s showing the maximum level it could be at, because when they sampled the water at the 24 hour mark in the salt water, Pseudomonas levels had dropped below the level where the equipment could detect it.


To summarize all of this: the epsom salt solution is an unfriendly environment for certain pathogens, like Pseudomonas. It also seems to have no effect on other pathogens, like Enterococcus.


What’s Going On Here?

float-fund-bacteria_Enterococcus_Thumb (1)Now that we understand the results, the first big questions is: what’s different between Pseudomonas and Enterococcus to yield such a large difference in their reaction to salt water and shaking?

Basically, Enterococcus is a BAMF. First off, it has specifically has been know to grow in salt agar mediums (which means that it doesn’t seem to be affected by salt in the same way as other bacteria). Enterococcus is also gram positive (it has thicker cell walls) as opposed to Pseudomonas (which is gram negative). Additionally, the lab folk at NSF International said that they had come across articles talking about how Enterococcus will actually secrete a substance to protect it from the outside environment, creating a kind of ‘shield’ around its cells.

In the end, we can’t be entirely sure why the difference is there, but our best guesses are listed above.

NOTE: The photos here are actually taken from the experiments discussed.

Float Lab’s Test Results compared to Float Fund Test Results

Previous to this test, there were other NSF conducted lab tests sponsored by Float Lab (a float tank manufacturer based out of Southern California). As mentioned above, the notable differences between our tests and theirs was the presence of shaking in the recent Float Fund tests.

Here, you can see the results from the Float Lab tests (no shaking) and the Float Fund tests (with shaking).

Float Lab (note: these numbers are all for tests in the epsom salt solution)

Float Lab Summary Table

Float Fund

Float Fund Summary Table

You can see from looking at these that the Float Fund test had a much stronger impact on Pseudomonas than in Float Labs test: a 2.58 log reductions vs 6.42. This shows pretty convincingly that mixing the epsom salt solution (as our pump systems do) heightens its hostile effects on certain types of bacteria.

You’ll also notice that Enterococcus reduced more over time in the Float Lab tests: a 0.76 log reduction vs 0.01 . This could be due to a number of factors, but the reduction of Enterrococcus, even in the Float Lab tests, is still very minimal and would not be enough to consider the salt water effective against it.

Our hats off to Float Lab for running their initial tests and opening up the data to the public so that we had the chance to build on it. This spirit of sharing, especially for the sake of collective improvement, is one that I hope the entire industry will continue to embody. These first salt water tests would have been more expensive, and more lengthy, without their initial data to start from.