Editors Note: This is a revision of a past blog post, updated to reflect the most current sanitation methods and standards.
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 safe and clean takes a fair amount of vigilance.
This post covers how we maintain basic water quality in the float tank, except for sanitization methods, which will be covered in its own beastly sanitation blog post. Stay tuned for that coming out next week!
I also recommend looking through the videos in our free water treatment course, which cover a lot of the material here in even more depth, and with visual aids.
Methods of Testing
There are several different methods for testing your water chemistry which are more or less commonly used. All of them have issues getting proper readings in our salt solution, for various reasons. We definitely hope that, in the future and as our industry grows, testing manufacturers will develop floatation specific methods that we can use.
Test Strips are most commonly used in residential settings, and if you’ve ever owned a hot tub this is probably what you used to test the pH, alkalinity, and bromine levels. Although they are quick and easy to use, we recommend that you steer clear of test strips. In many cases your health department will actually require that you use a different method to test your water. This is because test strips are very subjective (how dark does this orange look to you?) and leave more room for human error. The strips can also appear to be different shades depending on ambient light conditions.
Titration Kits are commonly used by center owners and health departments alike, and are generally considered to be a reliable source for water chemistry readings. Although the details vary from test to test, they involve mixing various chemicals in your water, and then counting drops to determine levels while you wait for color changes to happen. As with all other testing methods, the salt water still seems to interfere with the results of titration test kits (with a notable exception in the case of H2O2).
Colorimeters are used by adding reagents to water samples and then passing colored light through them to determine chemical readings. The density of the salt water seems to interfere with the refraction of the light, and in our experience, the readings from digital colorimeters can often be drastically different from sample to sample.
Electrodes are used to measure the conductivity or voltage of the water. Depending on their construction, they can tell about the presence of various molecules in water. These are commonly used in automated filtration setups, since they can continuously spit out data on ph, alkalinity, chlorine, H2O2, etc. without the need for manually running tests. There are no known electrodes that are calibrated for our magnesium sulfate water, so it is unknown if any are accurate in float tank water, although like the titration kits, they do seem to be consistent.
A Grain of Salt:
Although, at this time, the readings we get from our water chemistry tests might not be totally accurate, it is still important to test often and record everything. You’ll at least be able to see if your levels are trending up or down, and in combination with customer and employee feedback, you’ll be able to better maintain your water and address issues that arise. Even without 100% accuracy, regularly testing your water and recording the results is still extremely important for proper care of your float tanks.
pH and pHloating
As is the case with many things that we attempt to measure in our float tanks, the absurdly high concentration of magnesium sulfate seems to disrupt any standard form of pH testing. We don’t actually know of any easy method that is guaranteed to give accurate pH readings in our saltwater.
The uncertainty around these readings causes issues for halogen disinfectants like chlorine. Because chlorine and bromine rely on certain pH levels to be active, not knowing your true pH is obviously troublesome. However, if you are using a chlorine/bromine, pH will be one of the things that you measure at least once a day. Although the readings on pH aren’t reliable, they are at least internally consistent, so you can tell whether your pH levels are going up or down over time.
At Float On, 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 requires careful storage and care, and will need to be calibrated from time to time. We feel it’s a reasonable tradeoff for higher accuracy.
Like pH, it’s unknown whether there is anything that will get accurate readings for alkalinity in our salt solution. With alkalinity especially, we’ve heard back from several labs that it has been impossible for them to get accurate measurements, especially so with any equipment that is within the scope of what a float center operator would reasonably purchase.
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.
Since with both alkalinity and pH, we don’t have reason to believe that a specific method of testing is more accurate than another, we’ve chosen digital testing devices that are easy for our staff to use, and which seem to produce consistent readings over time.
We test the temperature of the water in our tanks three times a day with a handheld, precision reference thermometer. These are the badass thermometers that are often used to measure the accuracy of other thermometers.
Most standard handheld thermometers are rated to have an accuracy variance of +/- 1° to 2° 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 recommend spending more money on a reference thermometer that will have an accuracy of around +/- .08 degrees.
Many tanks come with built-in temperature probes: don’t assume that these readings are accurate! The instruments may need to be re-calibrated, and even then they may not give consistently accurate readings. This makes using the reference thermometer necessary to ensure that the temperatures are actually in that narrow range we’re trying to keep them.
Using a reference thermometer is also a good practice to get into as a safety measure, since it can prevent serious problems if your temperature probe starts running wild in one of your tanks. One of our tanks, for example, started getting up towards 100°, as shown on our reference thermometer, despite the built-in temperature readings coming back at 94°.
If you’re having issues with temperatures dropping when people aren’t floating, learn how to maintain temperature in empty tanks.
Along with checking the temperatures of the tanks, we also check the temperature settings of the tank heaters. As mentioned above, 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° F, but our heaters are all set to different temperatures to keep our water close to that target: the lowest is around 92° F, and the highest is set at 97° F. We had to experiment to find the right setting in each tank to keep the water from getting too cold or too hot.
Some tanks will allow you to calibrate your temperature settings so that you can correct them if they start to stray. This is nice for not having your temperature displays lie to you all the time, and you can use the reference thermometer to hone them in.
In most tanks, water temperature settings will have to be adjusted on a regular basis, even if they’re reading accurately. This is a practical result of certain floaters wanting the tank warmer or cooler, according to personal preference. Every adjustment to the controls should be noted, and every employee in the shop should know if a temperature has been adjusted, so that they will know to change them back when appropriate. If your shop, like ours, adjusts temperature settings regularly based on customer requests, 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 they’re available, the floaters might take it upon themselves to adjust the settings, which could ruin the experience for the next floater, or even create dangerous conditions.
This is an easy one – you simply want to make sure that you stay within the recommended depth range of your tank manufacturer. This usually between 9-12”, but is dependent on height at which the surface level skimmers, and other suction inlets on the filtration system, are effective.
At Float On, we measure depth with a plastic yard stick, putting it into the deepest part of the tank to get the measurement.
To adjust the depth, we simply add water through a hose (making sure that it’s being filtered in some way before going into the tank). Keep in mind that adding water will of course lower your specific gravity, since the ratio of water to salt will change.
WARNING: Running your pumps when the water is too low can result in serious damage to your pump systems.
In order to determine how dense (and thus how salty, and how buoyant) our water is, float operators use a tool called a hydrometer to measure the specific gravity.
A hydrometer is any device used to measure the density of liquids, but it most commonly takes the form of a weighted bulb and a stem with measurement markings on it. When submerged in a liquid, the hydrometer will float, and the stem will poke up out of the surface at a certain depth. The number that is right at the water’s surface is the specific gravity of the solution.
Specific gravity is the ratio of the density of our salt water to that of pure H2O (which has a specific gravity of 1.00). In a float tank, the range of specific gravity is kept between 1.23-1.30, with most centers running their tanks between 1.25-1.28 (which means most float tank solutions are 1.25-1.28 times as dense as regular water).
If the specific gravity gets too high (above about 1.30-1.32), your tank water will pass it’s saturation point and will be unable to absorb any more salt. Crystals will start to form, which can clog up your filtration system and cause your pump to seize.
If the specific gravity is too low (usually below 1.20-1.23) users won’t be as buoyant in the water. This can cause issues such as spinal discomfort and saltwater getting into users’ eyes (from their heads floating at a lower level in the tank).
We measure specific gravity twice a week, but we rarely have to add water and salt more than once a week.
Note: If you’re using glass hydrometers, hold them away from the tank when measuring. It’s an expensive mistake to have broken glass inside your float tank… or so we’ve heard.
Your flow rate is measured in Gallons Per Minute (GPM) or Liters per Minute (LPM), and is simply the rate that salt water is flowing through your filtration system. Flow rates are typically measured with a flow meter which is attached to the piping in your filtration system.
Flow rate will control the total number of volumetric turnovers you can do in your float tank in a set amount of time. This is important, since health departments require a set amount of turnovers in your float tank between each user – usually 3-5. (You can check out our health department essentials here.)
So if your float tank contains 200 gallons of salt solution, and your filtration system is doing 50 GPM, you’ll do a single turnover in 4 minutes.
3 turnovers would require 12 minutes.
4 turnovers would require 16 minutes.
5 turnovers would require 20 minutes.
Another reason measuring flow is important is to help catch any issues with your filtration system before they become too serious. If your flow rate drops from 50 GPM down to 30 GPM, there’s something wrong. Maybe there’s hair caught in your impeller, or something stuck in your filter, or a ball valve that’s not open all the way. Being able to check your flow rate at a glance can bring issues to light while you still have enough time to fix them.
GRAIN OF SALT: Because of the high specific gravity, it’s important to make sure you’re using a flow meter that is calibrated correctly to the salt water.
Gathering Water Samples
Because of the time it takes to do the various water chemistry tests, we carry around plastic, color coded, 125 milliliter vials with screw on caps to pull a sample of water from each of the tanks. We use these to run our tests in between floats so we don’t take up valuable transition time between customers. The vials are labelled with a number corresponding to each tank so that we won’t mix up the samples and forget which of them came from which tanks.
The filter PSI measures the amount of water pressure flowing through our filtration system in pounds per square inch. PSI is mainly used as an indication of how clogged up your filter is, and whether or not it is time to clean/change it.
GRAIN OF SALT: In pools and spas, you would typically change your filter after an increase of 8-10 PSI. However, we’ve found that our tanks don’t stay as clean if we wait for the appropriate PSI increase, which often takes 3-4 weeks. Instead, we change out our filters on a schedule of once every week to two weeks (depending on amount of floats run, size of filter, and manufacturer’s recommendations). As a result, we no longer regularly measure the filter PSI at Float On.
Clarity (or turbidity)
The water in your float tanks should be totally clear. If it’s cloudy at all, or discolored, that’s a sign that something isn’t quite right. In a float tank center, measurements of clarity or almost always done by eye with the aid of a bright flash light. In case you were curious, though, precise measurement of clarity is done in terms of turbidity, with an instrument called a turbidimeter (or nephthometer).
There are several different kinds of filters that can attach to a float tank, but most common are cartridge filters or bag filters. These serve a similar purpose, and are changed out on similar schedules. While cartridge filters can be cleaned and re-used for several months, bag filters are typically thrown out after each use.
Bag and cartridge filters should be changed based on your manufacturer’s recommendations, and on the volume of floats that you run at your center. At Float On, with our specific bag and cartridge filters, we’ve found that we need to change our filters every 1-2 weeks in order to prevent oils from building up on the surface of the water.
Draining and Refilling
There is no set schedule for draining and refilling float tanks, and although opinions vary, most commercial centers do a full swap of their salt solution every 6-12 months. We cover the details of draining and refilling a tank here, but basically you’ll be disposing of the salt solution, cleaning the tank and filtration system, and adding in new salt and filtered water.
Record everything and keep track of what you add
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-. We also record every time we alter the temperature settings or change filters. Over time, you’ll get a clear idea what measurements you should be getting for each of your tanks, 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. Drilling in this routine of water care is the backbone for any safe, successful, and sane float center.
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.
The 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]