How Long to Run a Filter Between Floats – DSP 356

How long should you run the filtration system for between floats? It’s an eternal question that has plagued float center owners since the dawn of time (Or at least until 1978 when the first float center opened up).

Ashkahn and Graham break down the science behind why you should filter for as long as you do and how to properly plan for it. This densely packed episode is filled to the brim with a summary of knowledge on water dilution, filtration, flow meters, and water sanitation brought over to float tanks from the pool and spa world. Take notes as you listen, there’s a lot to assess.

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A haunting image of the cryptosporidium oocysts

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Transcription of this episode… (in case you prefer reading)

Graham: Hey everyone. This is Graham over here.

Ashkahn: This is Ashkahn. Doing good.

Graham: You’re listening to the Daily Solutions podcast, in case the intro didn’t make that clear.

Ashkahn: I guess we didn’t really mentioned that explicitly, but I think you’ve got the right message across.

Graham: Is the feeling of it is there. We got some big news. Final episode is coming up.

Ashkahn: Coming up.

Graham: Which means it’ll be the last one and it’s going to be a doozy. It’s going to be a big one. We’re gonna do two straight hours. Unrelenting question answering. Coming up into this month.

Ashkahn: That’s right. November 29th, three o’clock to five o’clock. That’s how long two hours is.

Graham: Until, let’s say three to five since confusing.

Ashkahn: That’s pacific time.

Graham: That a good one. Otherwise they can be dead.

Ashkahn: And you can call in with questions and it’s going to be great. And we’re going to have information about like how you can call in and stuff. Eventually it will be or maybe right now in the show and that’s not really sure if it’s there then cool. If it’s not like we’ll get. It’ll be there sometime.

Graham: But going to go on our Facebook page, subscribe to our mailing list. Send us money. Wait, no, that one wasn’t necessarily. But if you all the other ones, you’ll be updated as to what’s going on when our live episode is.

Ashkahn: Cool.

Graham: Where to call?

Ashkahn: Cool.

Graham: So again, that was kind of rumbly, but the main thing, Thursday, November 29, 3:00 to 5:00 PM Pacific Time. Set it aside. It’ll be great.

Ashkahn: Hit it.

Graham: All right. And we got a question in the meantime which will kind of fulfill our obligation here is-

Ashkahn: It’s called Daily podcast thing.

Graham: Q and A podcast question is “I have 30 minutes between every customer. How long do I need to run my pump for? I’m following your advice of not running it while people are in the tank, but I don’t even like running it while they’re still in the room because of the noise.” I hear you.

Ashkahn: That’s the balance.

Graham: And it’s a pretty common situation too. Like I’d say, the most common transition time between customers is 30 minutes and that’s kind of the time from when you turn on the music for one person to get out of the tank till when the next customer has the room to themselves to kind of shower off and start floating, at least in our center. That’s what it means.

Ashkahn: And so there’s obviously a huge benefit to being able to run your pump for less time because it just means all of this goes easier for your transition and you can get people in earlier.

Graham: Ideally it would be instantaneous. You’re like bloop. And like all the dirty water goes in and just clean water is likes kksssshhhhh just in there.

Ashkahn: You’ll get a cool sound effects so-

Graham: But things don’t happen like that.

Ashkahn: Well, let’s talk about the basics.

Graham: I love basics.

Ashkahn: Pumps.

Graham: Actually what are we doing here? What are our questions? So, I mean, I guess first of all like, I think one of the basics is this idea of not running the pump when people are in the tank, which is worth mentioning again, and it’s something we’ve warned about on this podcast before.

Ashkahn: Oh sure. Don’t wanna do that.

Graham: It’s scary. It’s scary having the pump turn on when there were people in there.

Ashkahn: So there are things you can, there’s potentially a danger that a pump running while somebody inside the system could lead to what they call entrapment, where if a part of their body blocks the pipe sucking liquid in, that could cause them to be kind of vacuumed on to it.

If they don’t have some other pipe and or hair can get sucked up into a system like that these are kind of the dangers that are very realistic and could happen. There are ways to design float tanks that can alleviate those.

So this isn’t really like a universal thing. You have to look at your actual float tank and again there’s entrapment because of suction and there’s entrapment because of hair going through and different things like that to consider, but it’s a good thing to know about and to realize if your float tank doesn’t have those kind of safeguards and you really don’t want to be running the pump while somebody is in there because it could potentially be dangerous.

Graham: I mean one of the biggest things I guess to just know about your system and in my mind that can lead to especially kind of hair entanglement. Entrapment is just like if your pump is in the same room as the tank and they’re really close together, which it sounds like they are for the person sending in the question.

If the noise is kind of coming through and too loud then you have a very short distance between where someone’s head and hair is where the pump is. And I think that’s one of the scariest things. So I just wanted to, again, just wanted to mention it because I think that was a good aside and the question that’s worth highlighting.

Ashkahn: That was our scary fact for the episode.

Graham: So on to other basics-

Ashkahn: Pumps.

Graham: Filters.

Ashkahn: So all the stuff through pumps are pumping and pumping-

Graham: And filters are filtering. Ideally this is an ideal world we’re talking about here.

Ashkahn: Both those things are really true but the question is how are they pumping, how well are they pumping and how well are they filtering? So pumps are, are usually moving the liquid at a certain speed. When we’re here in the U.S we use gallons per minute in places that use the metric system, like the entire rest of the world. It’s liters per minute.

And so that’s how we’re usually measuring what they call the flow rate and basically this kind of number, this concept of how fast the liquid is moving is used in a lot of calculations to figure out how long you should be running your pump.

Graham: For sure and-

Ashkahn: And sometimes in some cases.

Graham: So there’s two different kinds of main systems that are used for float tanks and they sort of have different answers to this. Well, every float tank is going to have a different answer, first of all, there’s not like a set amount of time and then the water is filtered. It has to deal with all the details-

Ashkahn: There’s like two fundamental groups.

Graham: But the two big groups are having a reservoir type system where all the water leaves the tank and kind of goes through the filter to a storage tank and then back into the float tank from there. Then the other one is a-

Ashkahn: Recirculation system.

Graham: There we go. I mean I made a gesture and Ashkahn picked up that the word wasn’t coming.

Ashkahn: I get it.

Graham: Thanks buddy.

Ashkahn: It was an alley oop. So recirculation system is where the pipes and everything that the whole filtration system is connected with instead of emptying from the float tank into some external vat just connects right back into the basin of the float tank.

So the liquids just being kind of shot right back in. As soon as it goes through the whole filtration system.

Graham: And that’s the most common type of float tank.

Ashkahn: Here in the US, North America and in a lot of countries that we see those a lot more often.

Graham: I’d say just have manufacturers in the world.

Ashkahn: And it also that.

Graham: There’s probably like 90% of float tanks are recirculation and maybe 10% are reservoir.

Ashkahn: So the reason why those things are different is because of the kind of hydrodynamics of what’s going on in the float tank. What you’re trying to do is get the liquid in your float tank to go through your filtration system.

Graham: Sounds easy. What could possibly go wrong?

Ashkahn: So obviously the stuff in your filtration system is cleaning things and the liquid has to go through it. And so when you have this recirculation model where the liquid’s going right back into the float tank then that liquid is mixing with stuff that is standing there and hasn’t gone through yet.

And because it’s all mixing together and going and swirling around, it means you’re not really getting a uniquely a 100% of the solution in your float tank to go through the filter in a single pass. When you look at something like, “Hey, I have a pump that does 50 gallons per minute and I have a float tank that holds 200 gallons in it.”

Then simple math would say if every minute 50 gallons or going through this filtration system and if there’s 200 gallons in the tank, then in four minutes, 200 gallons have gone through. So all 200 gallons of my float tank have gone through. But obviously where that breaks down is the fact that everything is mixing together. So it means 200 gallons of gone through. But it doesn’t mean-

Graham: A unique 200 gallons.

Ashkahn: In the reservoir system. It is just kind of simple like that. Because you have a float tank, it’s literally emptying into an external vat.

Graham: So 100% of the water is going through the filter system,

Ashkahn: like it has to go through the filter system to get to the vat and then you do it back. So it kind of goes through two times.

Graham: In some systems.

Ashkahn: In some systems. Some systems just bring it right back. So that’s the logic that makes that kind of easier. So we kinda set those aside for a second because the complexity-

Graham: And if you have those then the answer is just however long it takes to go into the reservoir and back into the tank is how long your filtration needs to be-

Ashkahn: Pretty much.

Graham: Between people. Because then it’s all of it is gone through the filter. So that’s a simple one.

Ashkahn: Kind of.

Graham: So if you do a reservoir system done, we just answered your question.

Ashkahn: Will be some other things to say later about that. So just tuck it away, tuck it on the shelf for the moment and but remember that it’s there.

Graham: So recirculation systems then.

Ashkahn: So for the recirculation system, the question becomes, well how do we get more unique liquid to go through the system? And the answer is-

Graham: We listen to some guys from the 1920s called Gage and Bidwell who came up with the Gage-Bidwell law of dilution, which basically says that every turnover, not 100% of the solution in the float tank is going through a filter or when they were doing it for pools, just pool water.

Ashkahn: And the turnover, we forgot to say what that is.

Graham: Oh boy. That’s a little pastry. Typically something like apple or peach.

Ashkahn: It’s a turnover is what I described a second ago, which is you have a pump that does 50 gallons per minute. You have 200 gallons in your system. That means every four minutes, 200 gallons has gone through. You use that kind of simplified reality math to call four minutes a single turnover.

Graham: But we even like say it’s volumetric turnover I think is what that’s short for because it’s the full volume is being turned over. So what they pretty much did, was figuring out what the actual ratio of water that’s being mixed back in is.

And then from there you’d expect a certain amount of that to, during the next turnover of the filter system also get partially filtered. So anything that wasn’t touched during the turnover now part of that is actually going through the filter cycle and so that number ends up being 63% for when you’re doing a turnover with a pump.

Again, for them it was at a pool. For us it’s a float tank. 63% of the volume of that is actually going through the filter during a full volumetric metric turnover.

Ashkahn: And this is these are kind of statistics, so that means there’s a little margin of error there. But there’s a margin of error for all these things. But basically the more turnovers you do, the higher percentage of unique liquid going through the system that you get.

So for one turnover you get typically 63% going through. I think I usually like plus or minus 3%. When I see that number at two turnovers they say it’s 86% at three turnovers you’re up to 95% at four it’s 98% at five, it’s 99.3% at six it’s 99.7% at 10 it’s 99.99% and it’s never going to hit 100 because this is all just again kind of statistics approaching 100.

Graham: Sorry to break it to you people with recirculation pumps out there, but you’re never going to filter 100% of your water by the logic of this actually. You still have at least one little bit of water in there from the very first time-

Ashkahn: One drop just holding on.

Graham: That hasn’t been through your filter at all. So that’s kind of terrifying. Who knows what that drop of water holds.

Ashkahn: So that’s the concept. Basically the more you turn over, the better you’re moving all this stuff through your system.

Graham: I really wanted the end of that sentence to rhyme with turnover. Like the more you turnover, the more you grown over only like grown over would mean-

Ashkahn: Would have an actual real.

Graham: Exactly.

Ashkahn: That would have been cool.

Graham: I want to say to you can do this math at home if you have a piece of paper and a pencil too.

Ashkahn: And a computer. Just type it into Google.

Graham: But all of the right, it’s just you’re taking 63% and then you’re taking 63% of the remaining amount and adding that to the first 63% and then doing the same for the rest of it. So it actually just goes on-

Ashkahn: It’s called the exponential decay model.

Graham: It’s fun. If you have free time. I totally suggest it.

Ashkahn: I see the fun. So then the immediate question becomes, well, how many of-

Graham: Who are these Gage-Bidwells.

Ashkahn: Who are this guys.

Graham: No, you were going to say you.

Ashkahn: I like what percentage are we shooting for? And that’s where things get a little bit more complicated because there’s a couple of other variables here which is that the pieces of your sanitation system also only have a certain amount of efficacy.

So it’s not like a 100% of what goes through your filter is going to be perfectly filtered or 100% of what goes through your UV is going to perfectly be destroyed by the UV. So you also have to keep in mind that the rest of the components don’t have perfect 100% marks on them and that those percentages get knocked off of this kind of Gage-Bidwell logic for how effective these things actually are.

And the efficacy is not as generic as this other stuff we’re talking about because you’re talking about how good is your filter at filtering out some specific thing like cryptosporidium or how good is your UV at killing cryptosporidium that’s where you start using the kind of efficacy of those different things.

So it’s not quite the same but when we’re talking about filters and sanitation system is being effective and using those numbers you have to realize there’s kind of both those variables and that’s where the reservoir systems come back into play.

Graham: I have one more for these ones before we get into that.

Ashkahn: Well that was it. That was all I had to say about just that’s also affects reservoir system they also have filtration-

Graham: Never mind.

Ashkahn: Systems that aren’t 100% effective. So you have to also just remember that logic with those, even though 100% is going through. You put it back on the shelf now.

Graham: Wait, it was already on the shelf. You take it off-

Ashkahn: Take it off while I was saying that and then we can add it. Now it’s back

Graham: Now it’s back. I got it and I think I tracked it’s full shelf kind of path journey.

Ashkahn: Shelf life.

Graham: Wow, you got our audio engineer and recording with that one. There’s a shelf life was a winner. Cool. Wow, just made me forget it what I was going to say. Now here’s what I was going to say, which is that another thing to keep in mind is that if you’re just looking at the overall flow rate of your pump for how long you need to run your pump to get a single turnover, that’s also going to be affected by efficiency, which can be from turns in your pipes.

It can be from all kinds of the filter equipment that you put after it, so the best way to get the actual flow going through your whole system is by having a flow meter attached and specifically there’s one that’s calibrated. We’ll throw it in the show notes like we always do when we bring this up for float tanks so it’s giving an accurate reading as opposed to inaccurate for regular water.

And that a 50 gallon per minute pump for example, might only be getting 40 gallons per minute of flow or 35 gallons per minute of flow and at that point if you’d just done the straight math from your 50 gallon a minute pump in 200 gallon float tank, you think you’d need four minutes to do turnover and kind of calculate based on that.

But what you should actually be calculating off of is the true flow in your system. Otherwise you’ll end up renting your pumps for much shorter than  you should. So flow meters really important. Easy repair. Again, we’ve talked about this before, but we will include some cool show note links.

Ashkahn: And checking it as important because something might get clog up the system and lower that number and you want to fix that. So you’re getting these turnovers.

Graham: All right. Anyway, I realized we hadn’t said that one either for how to actually properly gauge the turnover rate there.

Ashkahn: This is where things get a kind of unfortunate. This is kind of the edge of the theoretical knowledge on this that you would look at for pools and spas and apply to pools and spas. And this is the point where we have to remind everyone that float tanks are not in fact pools and spas and assumptions that people make for pools and spas may break down when you start talking about float tanks.

So in talking to people who are kind of experts in filtration and have studied this stuff and know a lot more about it than we do. They’ve brought some other things up to us about float tanks that may kind of make this not really make as much sense or may not have this information be as reliable for us as it is for the pool and spa world, which is the hydrodynamics of what’s going on in a float tank maybe different than what’s happening in a pool or spa.

We don’t have some of the same kind of surface skimming equipment. The pools and spas do just because they’re typically really big, just literally big size wise, they’re too big to put on float tanks. They’re 14 inches tall or something that. So that’s one of the things we’re not-

Graham: Shallow end of the pool is always deeper than 11 inches is another way of saying it.

Ashkahn: So that’s one thing that we’re not using some of the same equipment to have that same sort of efficiency of what we’re filtering pools often balance their intakes to be sucking about a split of 25/75% from the surface versus from underneath the water. I don’t know, float tanks are doing that as the same or if they really should. Because the other weird thing about float tanks is that-

Graham: Everything floats.

Ashkahn: They’re float tanks, right. It may be much more important for us to. There may be a lot more on the surface of our systems that would otherwise sink in pools. Certain microorganisms may sink in a pool but a float in a float tank.

Graham: I don’t know of any research that’s been done on this, but it’s likely.

Ashkahn: But I mean, one person was telling us cryptosporidium this one that is a big thing in the pool world that people are always trying to deal with, is a little heavier than water. So it would sink in water but lighter than what float tanks are. So float in float tanks.

Graham: Likely float in float tanks.

Ashkahn: So that’s one thing. And their conclusion was that Gage-Bidwell might kind of break down in it’s logic when we can’t assume some of those things if we can’t assume that the same sort of mixing and surface balance and stuff like that as happening in a float tank versus a pool. We probably can’t assume that these Gage-Bidwell numbers are the same for us.

So I don’t know, I mean we don’t know research actually has to be done and things get specific per float tank and how they designed their intakes and outtakes and their skimmers and you can do tests where you put these little micro beads into your systems and actually see how many of them you’re filtering out and stuff like that. But stuff like that’s really expensive and some manufacturer has to pay a lot of money to do a test like that.

So that’s the sort of data that we don’t have right now basically that would help answer some of this stuff.

Graham: So we pretty much, we do the best that we can with the information that we have and what we can figure out is how much we’re actually pumping, which we can do with a flow meter. We can figure out from that what our actual turnover-

Ashkahn: If your flow meter is accurate.

Graham: If your flow meter is accurate, which-

Ashkahn: Not all of them are.

Graham: Again calibrated flow meter in the show notes. Just a little shout out for that. And so we have the volume, which means we can calculate turnover time, which means now we can figure out if we had 100% filter efficiency, everything else was acting normal, what percentage we’d expect to be getting with the number of turnovers, how much time we take to run those.

And that’s where we start to get into an actual specific answer for your question of how long should you run a filter for? So-

Ashkahn: So that’s the long answer. Short answer is 15 minutes.

Graham: Get out of here.

That was a total joke by the way. It ends up-

Ashkahn: It’s kind of a joke, but it’s also kind of like there is a thing that most people are doing, which is-

Graham: A lot of tank manufacturers are designing their systems to hopefully filter within 15 minutes.

Ashkahn: To do three turnovers. Is what a lot of people in the industry consider what that’s the basically the current kind of heuristic everyone’s using. We do three turnovers and a lot of manufacturers design their systems to accomplish three turnovers in around 15 minutes.

Graham: For sure. And I think like the majority of our tanks at Float On have to run slightly longer times with the pump in order to actually accomplish those three turnovers but-

Ashkahn: Certainly the ones we’ve messed with the filtration systems on, we have to run a little longer. We didn’t quite get them powerful enough.

Graham: But you never know, right? It can be that your tanks are taking longer. Some are actually designed with slower filtration kind of all the way through. And those, it’ll actually take longer to run a full cycle it might be that it’s 20 or 30 minutes to get even the three turnovers.

Ashkahn: And some places require more turnovers.

Graham: Four, five.

Ashkahn: The state of Washington requires, four. The state of Florida requires five.

Graham: That’s the highest. I don’t know anyone who’s above.

Ashkahn: It’s the highest I know. And then there’s like Australia that requires reservoir systems and like parts of Germany I guess. So there’s a couple things like that out there.

Graham: I don’t know specifically on recirculation systems though. I don’t know anyone requiring over five.

Ashkahn: Nor do I.

Graham: So that’s probably the range that you’re looking at is between three and five turnovers and I like to me it’s also a little bit of the vote in the confidence of what you’re doing further down the road and your filters and UV and what your cleaning schedule is on those. And just like how confident you feel in the rest of your system for three to five.

I mean you could do three and have a filter and no UV or something like that.

Ashkahn: Oh sure.

Graham: Or you could have a 10 micron filter versus a one micron filter. I mean these things.

Ashkahn: Or Chlorine as a residual and it’s just in the tank regardless of how much of your float tank solutions going through the filtration system.

Graham: That was perfect point.

Ashkahn: There’s definitely other variables that make this stuff mean different things in terms of sanitation.

Graham: And the ones that do have something where the disinfection is taking place as part, in line with the pump system. That’s where these things turnover isn’t getting all of the water through there and efficiency become really important. So if your primary disinfection is UV or ozone.

Ashkahn: UV especially.

Graham: UV especially.

Ashkahn: That’s the one that has the lowest reach, right? Like

Graham: Because it was Ozone will get blasted through a little bit.

Ashkahn: A little bit more. But UVs is really like it’s got to have contact time that UV chamber.

Graham: And chlorine you’re mainly worried about getting the hair and oils and things like that out during the system. I mean, they do help pull out other bugs that might be in there, but the chlorine fundamentally should be doing a lot of the heavy lifting for making sure that it’s safe.

Ashkahn: Cryptosporidium and Giardia, which-

Graham: Which we’re not as worried about in float tanks.

Ashkahn: Maybe.

Graham: Maybe. Well, I mean you have to swallow it. That is the nice thing about gastrointestinal bugs.

Ashkahn: You can but you only have to swallow one Oocyst of cryptosporidium to get sick.

Graham: It’s really fan word too if you want. And they look really creepy if you want to not sleep well at night. Look up cryptosporidium oocyst.

Ashkahn: That’s two o’s weird.

Graham: They look like little demons crawling out of an egg. It’s really creepy. We’ll put one in the show notes. So we have no idea how long you should run your pump for.

Ashkahn: Basically.

Graham: But there’s a ton of information for it. You can figure it out yourself. You can also probably call the manufacturer and they’ll tell you some information.

Ashkahn: Some of this is just this is it. This is as far as some people have figured stuff out. I don’t know, maybe manufacturers have other things they’ve heard from people and talk to people. So this again, it’s just information at this level gets more vague and conflicting and there’s just different experts out there kind of like giving their opinion.

Not like us, like different people who are like-

Graham: Much higher level.

Ashkahn: Who actually know what they’re talking about. People like who are like filtration experts who are just taking this in and making a guess of how they think it might work in float tanks that that sort of stuff is bound to be a little bit more of kinda variable until we get real data.

Graham: Until we get real data from float tanks and we’re not trying to generalize a bunch of pool information to it.

Ashkahn: So someday.

Graham: Good luck.

Ashkahn: Anyway, this podcast is ending.

Graham: Cool. I think that’s all I have to say today.

Ashkahn: Word.

Graham: All right. If you have a few last questions, run, don’t walk.

Ashkahn: Get on over. Go to the website.

Graham: Hitchhike a fast ride and take it on down to floattanksolutions.com.

Ashkahn: Type in a slash and then a podcast and you will be-

Graham: Hit the podcast button right after the slash button and-

Ashkahn: You’ll be all set.

Graham: Bam.

Ashkahn: Boom.

Graham: Talk to you tomorrow.

Ashkahn: Bye.

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