How to Drain and Fill a Float Tank

Do you ever wonder how all of that salt gets dissolved into a float tank?

There are roughly 850 pounds of epsom salt and 200 gallons of waters in an average sized float tank (approximately 8 feet long and 4 feet wide). It takes hard work (and a few tips I’m about to share) to get a tank ready for floating.

If you’re just opening your center, you usually don’t have a severe time crunch, and you can go about filling your tanks at your leisure. However, if you are an operating float center and are doing a complete change of your water, getting it done quickly is ideal.

Unless it’s your maintenance day and you’ve planned for the downtime, more time spent filling your tank can result in canceled floats and less money being brought into your business.

Based on my experience, here is the fastest way I have found to refill a float tank…

Disposing of Old Salt Water

The first thing you are going to have to do before refilling is to get rid of the old solution. Fortunately, because of proper sanitation and filtration, we don’t have to dump our water often: about once a year unless something unexpectedly goes wrong.

Here in Portland, we are allowed to dump our solution down the drain, and we run the hottest water we can behind it to stop any salt from solidifying. You don’t want the salt to just sit in your drain.

Always make sure to check in with your city before dumping your solution down your drains!

They’ll most likely be okay with it, but they might have a good reason for being cautious, and you should definitely make sure that they know what you’re up to.

A GRAIN OF SALT: Although we haven’t heard of any damage caused by draining our salt water solution down drains, we don’t ultimately know what the long term effects are. Just another reason to check in with your city first.

If your float tank uses under-tank heaters, make sure to turn these off before you drain it. They can burn out, or damage the tank, if they stay on with no water in the tub.

To drain a tank, I put a submersible pump into the float tank and pump the water out and down our shower drain. It’s pretty quick (a matter of minutes), not too loud, and doesn’t make a mess.

This pumping process won’t get out all of the water – you’ll probably be left with a quarter inch of salt water on the bottom. I normally get the last little bit of water out by using sponges to soak it up, and then wringing them out into a bucket. This actually goes by a lot quicker than you would think. We use sponges than can hold a pint of water, and it gets the job done fast!

You will also need to de-prime your pump to get as much water out of the filtration system as you can.

At this point, it’s probably worthwhile to actually take apart your spa pack to clean the pieces individually. At the very least, when you’re putting it back together, make sure to clean any salt off of the plumbing unions, especially the threads. Make sure to lube your O-rings and that everything is hand tight.

A GRAIN OF SALT: DO NOT run your pump dry! Running a dry pump can ruin it. We have signs that we place on our controls to ensure that anyone working the shop knows that there’s a water change in progress, and that they shouldn’t run the pump.

Show the Tank Some Love

The next step is to clean the inside of your tank.

Double check again to make sure your heaters are off while there is no water in your tank.

It’s rare to have a completely empty tank, and you can really get in there and disinfect everything and do some good scrubbing.

I normally like to use a solution of one part white distilled vinegar to one part water to clean up the salt. Then I’ll come back through with a solution of one part Simple Green to 64 parts water and clean the inside of the tank very well.

It feels really good to give some love back to your tanks!

Mixing Your Solution

This is where the real work starts…

I like to start the process off by filling the tank up with two inches of the hottest water I can get. Make sure to filter the water before it goes into the tank: depending on where you live, your municipal water quality is going to vary, and it is best to be safe and always filter your water. Mineral stains are a possibility if you use tap water and they do not look good. PLUS unwanted compounds can cause issues with your salt water.

After you have two inches of water in you tank, you can turn your heaters back on, which will help speed up the heating throughout the rest of the process.

Next, I add 200 pounds of epsom salt to the tank. From there I take a shower and hop in, using my body to mix up all of the salt in the tank (yup, you heard me). The water will begin to chill and will be much cooler after all of the salt is dissolved. After this, the height of your water will be right around two and a half to three inches.

This is the time to add more hot water. I like to add enough water to raise the height to about 4 inches. Add 200 more pounds of salt and get back in the tank to mix it all up.

The mixing is going to get more and more difficult as the water is not going to be as hot as the first mix and will take more time. Just keep mixing until the salt is completely dissolved. After the second mix, you will be at about 4.5 – 5 inches with 400 pounds of salt.

Add one more inch of hot water, 200 pounds of salt and repeat the previous step. You should be right around 7 inches of water now and 600 pounds of salt. One more inch of hot water to raise it to eight inches and 200 pounds of salt.

You will be at about 9-9.5 inches and just need the final push. Add about an inch of hot water and the rest of the salt to end up with a specific gravity of 1.27-1.28 and a height of 10.5 inches or the max height of your surface level skimmer.

A GRAIN OF SALT: You never want the height of your water to be above your surface level skimmer because they will stop being able to actually do their job skimming the solution.

You are not always going to add a perfectly round number like 850 pounds of salt. It is going to be completely random, maybe a little over 900, maybe near 1000 or a little under 850. It all depends on the size of your tank. I recently changed the water in our Ocean Float Room and ended up putting in 1200 pounds.

Another thing to note is that you may have to wait for your hot water to replenish. Adding in all of that water normally uses all the hot water you have and the water begins to run cold. You can still use cold water, it is just going to be much more difficult to dissolve and will probably not save you any time in the long run. I like to wait for the hot water to replenish and only put hot, filtered water into the tank.

Getting Back to Temperature

Once you have all of the salt and water mixed together, the solution is going to be pretty cold. I like to turn the heaters up and put a pool cover over the water. This traps the rising heat and causes the temperature to raise faster.

Check the temperature every few hours. Generally speaking, the whole process of draining the tank, to dissolving the salt, to having it back up to the right temperature will probably take about 12 hours. Most of that time spent is spent getting the tank back up to temperature.

The most labor intensive part should only take about 3 to 4 hours once you are comfortable with the process.

Measure Twice, Pour Once

Make sure that throughout the process you are double checking height and specific gravity so you have a gauge of how much more salt and water to add. The first time may be a frustrating and tricky, it just gets easier with experience. It used to take me a lot of thinking and time to get this done: now I can bang it out on autopilot and get it done quickly and efficiently.

Being aware of your specific gravity, it is very important. You do not want to end up with a high specific gravity because of damaging your pumps and you do not want to end up too low because it will affect floater comfort.

I like to reset the tanks at a specific gravity between 1.27-1.28 with 1.275 being perfect.

Double check that everything is dissolved. As your tank heats up, be aware that your specific gravity will probably rise as more salt, that couldn’t get fully dissolved in the colder temperatures, mixes into the water.

Salt can also collect in the middle of your tank on top of your heaters. This can cause them to overheat and burnout, and it will crystallize and harden your salt in the process, often making it dangerously sharp. Then you have to drain the tank again to change a heater and that is never fun.

The biggest lesson to take away is to just make sure all of the salt is 100% dissolved. It can be hard to see from outside the tank, so the best way to make sure of this is to just get in and feel around.

Did You Catch All of That?

To summarize, you are: draining your tank, cleaning the inside, adding hot water, adding salt, mixing and completely dissolving the salt and repeat the last three steps until you have a proper height and specific gravity.

Double check to make sure the temperature is back where it should be and that all of the salt is dissolved. Run the filter on your tank a few times through before you resume running float sessions.

We cover all of this and more at our monthly apprenticeship sessions. If you can’t manage to join us in Portland, feel free to contact us with any tank related questions you may have or check out our Water Treatment Course online (it’s absolutely free!).