chem geek

Non-chlorine Shock (mps) Dosing For Hot Tubs / Spas

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There have been several discussions recently regarding various ways of controlling organics and disinfecting hot tubs and spas. Though I've got a good understanding of the disinfection and the use of chlorine for disinfection (and the relationship of chlorine and Cyanuric Acid), I've always been a bit perplexed with how a weekly non-chlorine shock dose could work in a spa or hot tub. Also, there was usually little or no Combined Chlorine measurement yet that test is supposed to measure non-chlorine shock (potassium monopersulfate, MPS).

I wrote to Dupont (makers of Oxone which is the MPS in virtually all brands of non-chlorine shock) and received a response today that answers these issues. As I suspected, hot tubs or spas need a lot more MPS that should be added daily if used daily -- the once a week regimen will not oxidize the organics the rest of the week. So the benefits seen from MPS used on a weekly basis are only partial -- the full benefit should come from more frequent usage. Now keep in mind that this is coming from a manufacturer and that they have incentive to sell more product, but I think with some measurements from user's spas we can get to a reasonable recommendation.

The dosage recommendation for pools is 1 pound per 10,000 gallons one to two times per week depending on bather load which would correspond to 12 ppm of product (for each dosing) and should register as 2.5 ppm in a Combined Chlorine test (according to Taylor, one needs to mix and wait for one minute after adding R-0003; also to distinguish between real Combined Chlorine and MPS, one can use the K-2041 test which has R-0867 reagent). However, the non-chlorine shock (MPS) dosage for spas and hot tubs is 1-2 ounces weight (about 4 to 9 teaspoons) per 250 gallons which is 30-60 ppm and should register as 6.3 to 12.5 ppm Combined Chlorine and should be added after each use (or once per week if not used). This is much higher (3-5x) and more frequent (up to 7x) than what I had earlier recommended.

The higher MPS recommendation should help eliminate chloramine formation so there should be less "bad" chlorine smell during soaking (when ammonia from sweat combines with chlorine if MPS is not present) and it should reduce chlorine consumption somewhat. Also, if the bigger problem for hot tub covers getting degraded is the monochloramine which outgasses much more than chlorine (hypochlorous acid), then this should help. So, if anyone wants to try this new dosing amount and frequency, please let us know how it works out for you. Remember that MPS will measure as Combined Chlorine (if not separately measured with the K-2041 test) so with this more frequent dosing regimen you should be measuring Combined Chlorine virtually all of the time, but using MPS you will know that this is an MPS measurement and not "real" Combined Chlorine. If you get the Taylor K-2041 test then you can distinguish between the two.

Dupont also gave some broad guidelines for bather load where <1000 gallons/bather/day is considered high bather load; 1000-5000 gallons/bather/day is medium; and > 5000 gallons/bather/day is low.

So the regimen for daily or nearly daily usage of a hot tub or spa is to add both non-chlorine shock and chlorine after each use. The dosage for the non-chlorine shock is 4-9 teaspoons per 250 gallons. The dosage for the chlorine is about 1-1/2 teaspoons of Dichlor per 250 gallons during the first week or two and then 2 fluid ounces of 6% unscented bleach per 250 gallons after the first or second week.

Richard

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Wow. Thats an awful lot of product. I've heard of routines where non chlorine shock is added before each soak.

I've been using 1.5 tablespoons of non buffered MPS on a weekly basis for my 485 gallon spa per instructions on the bottle. I check weekly for combined chlorine before I shock. With normal use and my routine I register no CC. If my tub gets overwhelmed with soakers some night, I expect to have to shock with chlorine to eliminate chloramines. I have never measured MPS levels. I currently do not use ozone. Any thoughts on why I am not producing CC? With my old routine shocking with chlorine I would need to shock every other week because of accumulated CC. I just seems to me that my dosage of MPS is taking care of whatever oxidation needs to be done. Any thoughts?

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I agree it sounded high to me so perhaps the low end of the dose range can be tried and then measure CCs to see if they build up. If so, then lower the dosage. You ironically want a residual of CCs -- not real CCs, but what gets measured in the test unless you have the special kit to distinguish between real CCs and MPS residual.

The non-chlorine shock should never be used right before a soak. You should wait a little while -- at least 20 minutes -- before going into the water after adding the shock. It's probably better to add the shock after the soak, for similar reasons of doing so with chlorine so as to minimize your exposure so long as there is some residual still there when you get in.

With chlorine in the water, it can control CCs to some extent. Exposure to sunlight is the easiest way, but chlorine alone will breakdown ammonia -- it just takes time (at my recommended 4 ppm FC and 20 ppm CYA level, it takes about an hour to get to 80-90% completion -- it takes a lot longer if the FC/CYA ratio is lower). Chlorine combined with other organics can be more troublesome. At any rate, remember that there are multiple purposes for using the MPS. One is to control CCs, but the other is to prevent their formation in the first place to potentially reduce smell and damage to covers -- but this is theoretical and not proven yet. It was interesting that the longest lasting covers used daily MPS with weekly Dichlor, but I can't tell if the benefit is mostly from the more frequent MPS (eliminating monochloramine outgassing) or from the less-frequent Dichlor (reducing hypochlorous acid outgassing). So while in your situation the chlorine may be handling the CCs -- breakpoint for ammonia and minimal other organics -- you may still be outgassing monochloramine during your soak and for a while afterwards.

I don't mean to confuse the issue...I'm just trying to find a practical and useful regimen that both disinfects well, minimizes chlorine smell, and makes covers last longer. I'm guessing that some dose lower than what Dupont recommends would still lead to a residual of MPS that would be helpful, but we'll see.

Richard

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I'm a little confused... is this a regime for shocking with MPS when using chlorine as the primary sanitizer, or when using bromine tablets (which I know contain some chlorine) for the primary sanitizer?

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I'm a little confused... is this a regime for shocking with MPS when using chlorine as the primary sanitizer, or when using bromine tablets (which I know contain some chlorine) for the primary sanitizer?

I was talking about when using chlorine as the primary sanitizer, but the same regimen could be done with bromine, though I don't think that makes as much sense (i.e. it's not necessary). With bromine, you don't get the same sort of bromine + ammonia or bromine + organics problems that you do with chlorine so shocking frequently is not as needed. I can't speak to the issue of cover life since I don't know enough about the outgassing products of bromine but I suspect they are not as much of a problem as with chlorine.

I would say that it might make sense to use a somewhat higher dosage of MPS even when using bromine, but that it doesn't need to be added every day. Once a week would probably be fine and would serve the dual purpose of reactivating bromide to bromine and also oxidizing organics (and ammonia).

Please don't take any of this as gospel. I'm learning about this at the same time you are and it needs to be proven in real spas.

Richard

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I don't mean to confuse the issue...I'm just trying to find a practical and useful regimen that both disinfects well, minimizes chlorine smell, and makes covers last longer.

Richard

No problem. I appreciate the time and energy. Its all interesting info.

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Doesn't MPS dissapate to where your chlorine tests are accurate after a certain amount of time?

If there are organics in the water, then they will get oxidized by the MPS so the MPS will get used up. The MPS will also get used up if there is bromide in the water to activate to bromine. It may also very slowly reactivate chloride to chlorine. I don't know if it will break down on its own over time. So in practice, by going into the water regularly the MPS will get used up by the organics you introduce but if you get to the point where there is enough residual MPS because you add it frequently enough, then you should get to a steady see-saw state where you don't get to zero -- very much like you do with chlorine.

I can definitely tell you this -- I used MPS in my pool recently since I had an oil film (probably from suntan lotion) that wasn't going away with a scum ball or enzymes and though I know I've gotten rid of it before by shocking with chlorine, I didn't want to do that since my wife was using the pool almost every day. So I used MPS twice in a week and this not only worked to get rid of the oil film, but the chlorine usage cut to less than half what it was before. So if there are organics (and ammonia) to be oxidized in water, then this will lead to chlorine usage (though chlorine only oxidizes some organics better than others) and if you have enough MPS in the water instead, then it will get used up before the chlorine does.

I had heard the same thing you have that if you just wait 8 hours after adding MPS then you can measure chlorine accurately, but I think that's only a true statement if there are organics in the water that have built up so that within 8 hours the MPS level drops. If you keep adding MPS until all the organics are oxidized, then any more you add will build up and stick around and should register as Combined Chlorine. When I used MPS myself, this seemed to be the case after the second dose I added even the next day -- there seemed to be a small amount of persistent Combined Chlorine and that's not something I usually see. It did go away by the following day, but my wife had used the pool so more organics were introduced so all the MPS could get used up.

I suppose a simple experiment would be to take some pool or spa water in a bucket, add a very small amount of MPS, and see if a persistent CC is measured and how long it lasts (if it doesn't show up initially, add more MPS until it does).

Richard

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Just got my Taylor K-2006 in! Thanks for the reccomend on those kits. Strips are pure garbage. Do you have a MPS addition table based on combined chlorine? I don't want to just add willy nilly now that I have a nice test kit. Thanks!

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Just got my Taylor K-2006 in! Thanks for the reccomend on those kits. Strips are pure garbage. Do you have a MPS addition table based on combined chlorine? I don't want to just add willy nilly now that I have a nice test kit. Thanks!

Assuming that the Combined Chlorine is measuring the MPS and not real Combined Chlorine (and that's a reasonable assumption when using MPS since it will prevent Combined Chlorine from forming in the first place) and if you are following the procedure shown in this link from Taylor under "Monopersulfate Compound Test" where you skip the FC measurement and add the R-0003 right after adding the powder and swirling and then wait one full minute, and then subtract that from your Free Chlorine measurement (you won't be able to separately measure true Combined Chlorine unless you get the K-2041) then you can measure MPS reliably. You measure the Free Chlorine (FC) the normal way in your K-2006 kit -- the interference remover for MPS is really for removing the interference in the CC measurement -- MPS shouldn't affect FC unless you test FC really slowly.

The non-chlorine shock is 614.77 g/mole but since it isn't pure, the effective molecular weight is 680 g/mole where each mole has 2 moles of persulfate and each of these corresponds to one mole of Combined Chlorine and all chlorine is measured as chlorine gas equivalent at 70.906 g/mole. So 1 ppm (mg/liter) of Combined Chlorine is (1/70.906)*(680/2) = 4.8 ppm of non-chlorine shock. Dupont is saying they recommend a dosage of 12 ppm non-chlorine shock for pools once or twice a week and 30-60 ppm for spas once after each use or once per week if not used. I think their spa recommendation is on the high side, but that is due to the high bather load (bathers per water volume). So their recommendation would be to register about 2.5 ppm CC in a pool after a weekly dose while a spa would show 6.25 to 12.5 ppm CC after a dose after usage. I think that's higher than you need and if you just add enough MPS after you get out so that you still have reasonably measurable (about 1 ppm; perhaps a little less) CC when you next get in, then that should be enough. You can let us know how much MPS that ends up being.

Adding 1 ounce weight of MPS to 350 gallons adds 28.35 grams in 1325 liters or 21.4 ppm (mg/l) so 4.5 ppm CC so you can scale down accordingly knowing that the density of MPS is around 1.3 g/ml which is roughly the same as ounces weight per fluid ounces. So 1 ounce weight is roughly 0.77 fluid ounces which is about 4-1/2 teaspoons. So 1 teaspoon of non-chlorine shock adds about 1 ppm "CC" equivalent in 350 gallons.

Richard

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I appreciate the work you put into this! It's to bad this site doesn't allow posts to be made stickied at the top as a lot of yours should be! After reading your posts maintaining a chlorine tub is so much easier. Having a real test kit is the cats meow!

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ChemGeek, I know this is an old post but your recommendations for adding MPS -are they the same in a bromine spa?

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In a bromine spa you presumably have created or built up a bromide bank so the MPS will slowly oxidize bromide to create more bromine. So the dosage is really to create a bromine level or to add enough to oxidize bather waste.

The rough rule-of-thumb with no ozonator is that every person-hour of soaking in a hot (104ºF) spa requires around 3-1/2 teaspoons of Dichlor or 3-1/2 fluid ounces of 8.25% bleach or 7 teaspoons of non-chlorine shock (43% MPS) to oxidize bather waste. That is true whether it's a chlorine or a bromine or a Nature2 silver ion spa. With an ozonator and heavier bather load (i.e. soaking every day or two) these amounts might be only half as high. The real rule is to add whatever is needed so that you end up with a residual of disinfectant 24 hours later and then maintain that level prior to your soak. That's usually around 2 ppm Free Chlorine (FC) for chlorine or 4 ppm Total Bromine for bromine.

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Thank you!

We have an ozonator but it's also a vacation rental that sleeps 8. Our maintenance guy comes after each group leaves but I'm wondering about asking guests to add a small amount after each use.

With a silver ion cartridge I thought bromine should be 1-2?

When you shock, should the level temporarily go really high or should it go from the 0 that it probably was to what a normal reading would be?

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If the ozonator is working, then maintaining a bromide bank -- around 30 ppm bromide -- should have the ozone maintain a background level of bromine. The ozonator should oxidize bather waste so need only half the amounts (or less) that I indicated when there is bather load. Then the issue will be what to do if the spa has heavy use. It will need some sort of oxidizer added to it to create more bromine -- chlorine or MPS.

If you shock, it goes high not just to normal. The problem with adding too much is that it will take time to get lowered but if you add the right amount after a soak then it should drop down to normal within 24 hours. So managing a vacation rental is tough, but at least the ozonator helps.

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Thank you.

And that is the problem -we don't have a 24 hour window ; we have a six hour window between guests although I could start arranging it the other way.

I interviewed one maintenance man who is certified/licensed ( took the classes) and he didn't think a bromide bank was necessary! But then I discovered it isn't with the bromine tablets , although you will start out with a chlorine system for awhile then.

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You don't need a bromide bank when using tabs TO MAINTAIN A BACKGROUND LEVEL, but you definitely need it at first if you want to shock to raise the bromine level quickly. Over time, the spent bromine from the bromine tabs will build up a bromide bank BUT ozone oxidizes some bromine to bromate so there is a battle going on between the bromine tabs adding bromine going to bromide and the ozonator both creating bromine from bromide AND turning some bromine into bromate where it remains as such. So as for what goes on with your bromide bank is unclear -- who wins out, the ozonator creating bromate or the bromine tabs adding more bromide from spent bromine. Unfortunately, there's no easy test for testing bromide explicitly.

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Hey Chem Geek, thanks for the years of helpful information. I've had a hot tub for 5 years and have read a lot of your posts. I pretty much use Nitros approach to maintaining my spa. Its worked well, but the one thing that I've always been a little fuzzy on was the use of MPS shock. He recommends using MPS sparingly. My routine consists of filling the hot tub with soft water(my hard water is off the charts). Then I add calcium to get it to 200. I add my acid to get the ph right and get the chlorine to 10. I also add a half bottle of Gentile Spa. After a couple of weeks I make the switch to bleach. I try to keep my chlorine levels at 3-6 and once a week I would shock with either bleach or MPS. I used MPS every now and then but really have no idea of what levels to get at or how to even test the levels. I have the standard Taylor kit that doesn't measure MPS so I was kind of guessing. I have a 480 gallon tub so I might add 3 tablespoons of MPS the weeks I used it, if I used the tub a bit. Anyway, I would like to start using MPS more and maybe keep the chlorine down a bit to help with the chlorine smell and vapor barrier of my spa cover lasting longer. I've read this post but I'm still a little confused as to what combined chlorine is. Also, when I add MPS, does this register as free chlorine? I assume FC is what I'm testing with my Taylor kit. How do I test for combined chlorine and what does it tell me? Can you dummy it down a little for me and in detail tell me what I need to do. Such as, get the k-2041 kit and test and keep the mps levels within this range, shock with MPS once a week to this level and add bleach as needed and keep at this level. As I said, my regiment has worked, but I would like to minimize the chlorine smell. Any help is appreciated.

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Ok I figured out how to test for combined. I have no idea why I never tested this using my Taylor kit. So does the MPS only effect the combined and not the Free? Do you have guidelines as far as your use? Such as you and your wife soak twice a week for 20 mins, what is your maintenance as far as bleach and MPS?

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I tried using MPS like Nature2 recommends for a month or so. I would add about 1 tbl to my 200 gal tub after every soak 3 to 4 days a week. I used test strips that showed a residual amount left after 24 hours like they recammend. This seemed to work well with the small amount of Dichlor and copper ion product I was using. The problem was that the MSP was very acidic. I had to add to add Borax or Washing Soda constantly to maintain proper PH. This was a lot of extra work. I started to add equal amounts of Borax which seemed to work okay. But that's a lot of Borax. Using Baking soda raised the alkalinity to much. Washing Soda required more to achieve similar results to Borax and also raised the alkalinity.

I've since switched to Nitro's system. My PH is consistent and my CC's are .5 or less. I've tried using MPS after a soak every once in a while but it always lowers my PH a bit. I'll probably use it once in a while if my PH is high because I have a lot left. I had hoped I might be able to use less chlorine and use MPS to oxidize bather waste post soak. But the way it affects PH is a hassle.

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I thought it would be helpful to add my experience to Richard's comments on the subject of ozone in a bromine spa

If the ozonator is working, then maintaining a bromide bank -- around 30 ppm bromide -- should have the ozone maintain a background level of bromine.

absolutely right. in my 2013 Grandee, the corona discharge ozone generator is capable of maintaining a small ( less than 1ppm) background level. However, in order for this to happen, there must be no bather or residual load, and no bio contaminants present. A stray spider, bee, pollen from nearby trees or other organic matter that might find its way under the cover can upset this balance very quickly, and if the ozone generator is not able to keep up with the additional load, the spa will quickly return to a zero sanitizer level which is not a good thing.

But right after a good Ahh-some purge it works beautifully, especially if the cover fits well and there are no dust storms :D

If you shock, it goes high not just to normal. The problem with adding too much is that it will take time to get lowered but if you add the right amount after a soak then it should drop down to normal within 24 hours. So managing a vacation rental is tough, but at least the ozonator helps.

for sure. with a modern (late model) truly "clean" bromine spa with a strong corona discharge ozone in use (my Grandee for example), the sanitizer decay rate can be substantially less than 25% over 24 hours and the decay behavior appears to be rather asymptotic. I've measured as low as 10% decay rate when the sanitizer level is in the upper single digits, so you can see that it can be a lot more than 24 hours if you don't get the dose right!

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The problem in a vacation rental is we don't have 24 hours to let the sanitizer get down to normal. We have a 6 hour window between guests. (Unless I want to change that and never have changeover days-where one group leaves and one comes in the same day).

Another question- we aren't getting 4-6 months on a fill. More like 4-6 weeks! But I guess it's because of the bather load in a vacation rental. It seems to get cloudy and/or foamy right away (from lotions/sunscreens?) and you can only add so much clarifier and defoamer before refilling.

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Yea I can see the challenge. Its not hard to imagine the very high bather loads associated with a vacation rental, not to mention the oils and sunscreens as you mention. So the 4-6 weeks water life doesn't surprise me. How much time to you reserve for draining and refilling when it's time to do that? Sorry if you've already given this information, but how large is the spa (gallons), how many people use it during their stay, for how long, and do you have a rigorous education session prior to each rental?

I'm struggling to offer something useful here, in terms of a suggestion, but the only things that come to mind are:

1. maybe you should in fact consider a 24 hour change-over time just to guarantee the spa's condition for the new guests, and to assure them that you take meticulous care of the spa. If someone got sick, for example, 6 hours isn't enough time to do anything major like draining, purging, ,or a decon. What do you do today in that situation?

2. Pardon the question, but are you using Bromine, is there an ozone generator, and have you considered chlorine? I don't know about doing this on a regular basis, but at least with a chlorine spa you can correct an "overdose" with peroxide.

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Thank you for all that!

We have a 375 gallon , 6 person tub, just 4 months old. We use bromine and have an ozonator.

Our rental sleeps up to 8 but I may start limiting it to 6. It's rented about 60 nights during the 3 summer months, and about 130 nights a year.

I don't know what you mean about an education session- we just have a sheet of paper they read and sign and it's also hung up at the rental.

Our service person says he'll come by noon and they'll be able to use it by 3:00-4:00. Even if it got to 10 with the shock, can't it be used before it gets down to the ideal of 3-5?

It drains quickly but it took about 9 hrs to warm up again last time.

I asked the other owner I know there if she ever gets 4-6 months on a fill and she said no-

"It varies greatly on how often we drain tubs. Sometimes it is after one stay and then the most we go is probably 3-4 weeks.

Our personal tub we could go 3-4 months and just drained it because it was time, not because it looked bad.

So many guests go out during the day hiking and have on all of the sunscreen and then come back and get in the tub without showering. It really makes a mess, and in winter it will be moisturizing lotions, but not as bad as sunscreens. Kids seem to always really mess up the ph."

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Well, I have personally used my own spa at 10ppm bromine, but that isn't recommended especially in a commercial situation! I did it to introduce a sanitizer demand (lol) to lower the level quicker! But you really need to stay inside of established commercial norms its seems to me, as people do pay to use the spa which means its "commercial" in that sense, although I don't pretend expertise in this area. 62..5 gallons per person is a very very heavy bather load, so I wouldn't expect much life out of the water at all :D

about the shock. I don't think you can, frankly, and here's why: Suppose you shocked to 10ppm (bromine) -- that is only slightly higher than the 4-6ppm normal range accepted for Bromine so it really isn't a shock at all, its just over-sanitizing :D. But 10ppm is higher than acceptable and people with any sensitivity to halogens could be affected, so you have to achieve 6ppm before the new guests take over the spa. With ozone in use, and sodium bromide salts in the water (as chem geek discusses above) your normal decay rate (with no bather load and no residual from the guests) would require 3 days to decay back to 6ppm! But the thing is, you DO have residual bather waste from the previous guests; you just don't know how much , so you cant really determine what shock value to use, and you don't know how much sanitizer they already added before they left. So what I'm suggesting is that you just forget about shocking -- just raise bromine level to 6ppm asap when the guests leave and measure it frequently over the next few hours to maintain 6ppm while you adjust other stuff. You want 6ppm, the top of the acceptable range, when the new guests arrive.

what is your bromine delivery method?

as for education, i was thinking of a personal 10 minute face-to-face training session to make sure the guests know how to add bromine or to adjust any other parameters that might go wacko under such a heavy bather load, but written instructions I'm sure will work (if they have questions they would contact you). do you have the guests adjust pH as well?

have you considered establishing a requirement that guests shower before entering the spa? it would be the honor system, but better than nothing

another thing to consider, since the spa is SO heavily used and by a great variety of people over a short period of time, is to purge it every time you drain. here on this forum we have found (experimentally) that the product called 'Ahh-Some' is a very good purge product, as verified by my own personal story as well. Just add the correct amount of the product (follow label directions) to the spa before you drain. combine that with a 20-ish ppm bromine shock. in the afore mentioned article, I had a well-maintained spa with clear water in great shape (low bather load), and no unusual sanitizer demand and I STILL released copious amounts of waste from my spa with an Ahh-some purge, so I'm now a believer in purging frequently and especially in a commercial situation I would purge every drain.

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