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


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#1 chem geek

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Posted 30 October 2007 - 10:13 PM

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

#2 tony

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Posted 31 October 2007 - 04:27 AM

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?

#3 chem geek

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Posted 31 October 2007 - 08:02 AM

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

#4 Whoneedsavacation

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Posted 31 October 2007 - 10:09 AM

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?

#5 chem geek

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Posted 31 October 2007 - 11:42 AM

QUOTE(Whoneedsavacation @ Oct 31 2007, 11:09 AM) <{POST_SNAPBACK}>
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

#6 tony

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Posted 31 October 2007 - 01:40 PM

QUOTE(chem geek @ Oct 31 2007, 12:02 PM) <{POST_SNAPBACK}>
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.


#7 wireman

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Posted 07 November 2007 - 06:37 PM

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

#8 chem geek

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Posted 07 November 2007 - 11:17 PM

QUOTE(wireman @ Nov 7 2007, 06:37 PM) <{POST_SNAPBACK}>
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

#9 wireman

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Posted 13 November 2007 - 07:32 PM

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!

#10 chem geek

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Posted 13 November 2007 - 08:27 PM

QUOTE(wireman @ Nov 13 2007, 07:32 PM) <{POST_SNAPBACK}>
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

#11 wireman

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Posted 16 November 2007 - 06:12 PM

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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