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How to Test the Quality of Float Tank Water

In a perfect world, you could just pour water and salt into a float tank and it would stay pure and clean and fresh and salty forever. In the real world, conditions in the water are constantly changing, so keeping your water in perfect condition takes a fair amount of work and vigilance.

Water that isn’t maintained properly can lead to bad float experiences and become unsanitary and unsafe.

We test the condition of our water twice a day using a variety of measurements, basically one for every important variable water condition. Because some of our tests take a bit of time, we gather water samples from the tanks in between floats and perform measurements later when we aren’t busy transitioning rooms and checking in floaters.

Everyday, we check the following conditions in our tanks – temperature, temperature setting, filter psi, water depth, specific gravity, hydrogen peroxide concentration, alkalinity, and pH levels.

testing float tank tempsTemperature

To test the temperature of the water in our tanks, we use a handheld, high resolution, precision reference thermometer. These are the types of thermometers often used to measure the accuracy of other thermometers.

Most handheld thermometers are rated to have an accuracy variance of +/- 1 to 2 degrees f. This won’t cut it in the world of float tanks where a difference of only half a degree might be enough to ruin a float. So we opted to spend more money on a reference thermometer with an accuracy of around to +/- .05 degrees.

Many tanks come with built in thermometers. Do not assume that these readings are accurate, they may need to be calibrated and re-calibrated. We have built in thermometers on four of our six tanks, and none of them are currently accurate. That is why we use the reference thermometer. If your temperatures are not ideal, learn how to maintain empty tank temperature.

Temperature Setting

Along with checking the temperatures we check the temperature settings of the tank heaters. We quickly found that the temperature setting is not an accurate indicator of how much the heaters will actually heat the water. Our target temperature is 93.5 degrees f, but our heaters are all set to different temperatures to keep our water close to that target, the lowest is around 92, and the highest is set at 97. We had to experiment to find the right setting in each tank to keep the water from getting too cold or too hot.

Every once in a while the settings will have to be adjusted. Maybe a floater wants the tank hotter or cooler, or maybe the door was open and the tank got too cold and someone needed to get the temperature up in a hurry. Every adjustment to the controls should be noted, and every employee in the shop should know if a temperature has been adjusted outside of normal settings, so that they will know to adjust them back after the temperature has returned to normal. It’s a good idea to check the controls routinely, in case someone has changed the temperature and forgotten to change it back. Temperature controls should be inaccessible to floaters – if not the floaters might take it upon themselves to adjust the temperature for you which could ruin a float or even create dangerous conditions for the next floater.

Filter PSI

float tank pump psi

The filter psi measures the amount of water pressure flowing through our pumps in pounds per square inch.  The reading is taken from one or two pressure gauges (two if you want to measure pressure pre and post filter) attached to the filter system. Filter PSI readings can indicate whether your pumps are functioning properly, getting the required level of flow for proper filtration, or if the system is in need of a filter change.

Water Depth

This is an easy one, we take a plastic yard stick and stick it into the deepest part of the tank to measure the depth. We try to keep the depth of our water between 10 and 11 inches.

Specific Gravity

measuring specific gravity in a float tankIn order to determine how buoyant (and thus how salty) our water is, we use a tool called a hydrometer to measure the specific gravity.

A hydrometer is a weighted glass bulb and stem with measurement markings on it. We fill up a graduated cylinder with tank water, then sink the bulb of the hydrometer into the water so that it sinks as far as it can without touching the bottom of the cylinder. The stem of the hydrometer is then poking up out of the water, and the number that is right at the waters surface is the specific gravity. It’s important to note to hold the hydrometer away from the tank when measuring. It’s an expensive mistake if you hold it over the tank and drop it… or so we’ve heard ‰

Specific gravity is a measurement of the ratio of the density of our tank water to that of pure H2O. We try to keep our specific gravity around 1.280, meaning our salty tank water is 1.28 times as dense normal water. If the specific gravity gets too high your tank water might pass it’s saturation point – it will be unable to absorb anymore salt and crystals will start to form, which can clog up your impeller and cause your pumps to seize.  If the specific gravity is too low it makes it harder to float.

Gathering Water Samples

float water hardness testing

Because of the time it takes to do the next three tests, we carry around plastic color coded 125 milliliter vials with screw on caps to each of the tanks and pull a sample of water from each to test in between floats. The vials are labelled with a number corresponding to each tank so that we won’t mix up the samples and forget which came from which tanks.

Why We Avoid Test Strips

The next three tests for Hydrogen Peroxide, Alkalinity, and pH levels are often performed with test strips at other float centers. While test strips may be fine in general, we felt like reading them could be too subjective (how dark does this color orange look to you?) and left more room for error than we were comfortable with. More importantly most health departments don’t accept test strips due to their subjectivity. The strips get old and stop working properly, they can get contaminated, they appear darker or lighter depending on ambient light conditions, etc. So at our shop, we decided on more accurate, more labor intensive testing methods that left less room for subjectivity and error.

Hydrogen Peroxide (H2O2)

We use Hydrogen Peroxide (H2O2) as a sanitizing agent in our tank water, and try to keep the levels at 100ppm. It’s important to make sure it doesn’t drop too far below 50 ppm. Too much hydrogen peroxide can irritate the skin of some floaters, and also may cause little bubbles to form due to oxidation which can tickle the skin. And of course if there is too little H2O2 it won’t be an effective sanitizer. It’s important to follow proper usage and handling procedures of H2O2.

To measure our H2O2 levels, we use a titration kit.

h2o2 testing in a float tankThe titration kit includes several reagents, or chemicals, to add to a water sample to cause a certain reaction, and a titrant, which is a chemical you add drop by drop in order to achieve a visible reaction (most likely a change in color). The number of drops it takes to achieve a visible reaction indicates the percentage of H2O2 (or whatever chemical you are measuring for) in the solution.
The kit we currently use involves adding 3 reagents to a 25 ml water sample which turns the water a dark blue or grey, then adding the titrant drop by drop and counting the number of drops until the water goes clear.  We then multiply the number of drops by 5, and that gives the H2O2 saturation in parts per million (ppms). [note: This was a LaMotte test kit – we are now experimenting with a Taylor H2O2 test kit at Float On, which has a similar but different method – Graham Talley, 1/2/15]


For our alkalinity test, we use an Alkalinity Colorimeter. It’s a little device that holds a water sample and shoots a beam of light through it. You then add a reagent to the same sample, put it back in the machine, it shoots the light through it again and gives an Alkalinity reading based on the difference between the light readings before and after the chemical reagent is added. We try to keep our Alkalinity between 80 and 120.


We measure the pH using a digital handheld pH meter. This is a fairly easy to use device, we just dip the tip into a water sample like a thermometer. It does take the machine a minute or more to settle on an exact reading, which is why we test samples rather than test the water directly in the tank. The digital pH meter also required careful storage and care, and will need to be calibrated from time to time. We feel it’s a reasonable trade off for higher accuracy. We try to keep our pH around 7.5, as most regulatory bodies consider 7.2-7.8 the ideal range.

Record everything and keep track of what you add

Float Tank Measurement Tracking

After we take all these measurements, we record them using our Helm software. In addition to measuring the water conditions, we also record and track the amounts of chemicals we add to the tank (water, salt, H2O2, alkalinity up, ph+ or ph-) and every time we alter the temperature setting or change filters. Over time, we get a clear idea what measurements we should be getting each morning, of roughly how much H2O2 to add daily, how much salt to add weekly, how often to change filters, and so on.

With enough data and accurate measuring methods, you can eventually dial in a routine that will allow you to maintain proper conditions in your float tanks day in and day out, ensuring a safe, healthy, and comfortable float each and every time.


A Grain of Salt –

It’s worth noting that at this time in float tank history many of these testing methods have not been tested by their manufacturers on actual float tank water. This means the readings we get from these tests might not be give exact results, which is all the more reason to test often and record everything. You’ll at least be able to see if you levels are abnormal, trending up or trending down, and use what you know about your water control methods in combination with customer and employee feedback to figure out what works and what doesn’t. Even without 100% accuracy, regularly testing your water and recording the results is still extremely important in maintaining the quality of your water.




Original author: Marshall Hammond
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