Shocking does not work...help please.

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S

somaholiday

0
Jan 24, 2008
10
Hey all...

Shocked my pool recently, CC was up to .8. I checked multiple sources and they all came to the same amount of a little over 13 gallons of sodium hypo (I run a 200,000 gallon indoor pool). I dumped 15 gallons for ease of measurement and assurance of reaching the breakpoint, and I also turned all of my exhaust fans on full bore.. Next day I came in and the CC only went down to .6. Do I need to stay here overnight and keep the PH steady at 7.2? I can't think of anything I'm missing.

Normal ranges:
fc 3ppm
cc <.5 (IM TRYING)
ph 7.4 (dropped to 7.2 with acid before shock, just didnt keep it there)
alk 80-90
cal 400-420
temp 82-83

Thanks a lot.
 
Soma,

Welcome to the forum. I'm not an indoor pool guy so wait for the gurus in that area to come along. That said, it's my understanding that MPS is a little more desireable shocking agent than chlorine in an indoor pool. There'll be more clarification soon.
 
15 gallons of 12.5% chlorinating liquid (assuming that is what you used) in 200,000 gallons would add 9.4 ppm Free Chlorine (FC) to whatever level you started with. That is more than enough to achieve breakpoint with monochloramine. In fact, the 10x rule isn't even correct, but I won't get into that here. The problem is that the Combined Chlorine you have in the pool is probably chlorine combined with other organics (not ammonia/urea) and those may be hard to "break" and can result in persistent combined chlorine which is what you are seeing. This is rather common in indoor pools, possibly due to the lack of sunlight (since UV may help break down some combined chlorine) and possibly due to a lack of Cyanuric Acid (CYA) in the water (more on that later).

As Dave pointed out, the use of a non-chlorine shock, potassium monopersulfate (MPS), is normally done to prevent the formation of combined chlorine and can, to a lesser extent, be used to try and remove combined chlorine though it isn't particularly good at that "after the fact". There are also "designer" MPS-like products that can very powerfully remove virtually all organics from the pool (see Truox, for example), but both MPS and these designer products are expensive.

Now, back to CYA. CYA is not normally used in indoor pools because it is thought, mistakenly, that its only purpose is to protect chlorine from breakdown from UV rays in sunlight. Though this is one role for CYA, it is not the only one. CYA combines with chlorine rather strongly so that at normal ranges such as 3.5 ppm FC with 30 ppm CYA, about 97% of the chlorine (FC) is in the form of chlorinated cyanurates -- that is, chlorine attached to CYA. Only 1.5% is hypochlorite ion and only 1.5% is hypochlorous acid (at pH near 7.5) with only the latter being the effective disinfectant and oxidizer. ALL reactions with chlorine are slowed down by orders of magnitude when CYA is present. Or put another way, ALL reactions with chlorine are sped up significantly when CYA is not used. This includes destruction of swimsuits (especially reduction of elasticity of rubber and fading of non-fade-resistant fabric), flaking of skin, frizzing of hair, corrosion of metal, and generation of disinfection by-products including nitrogen trichloride, chloroform, and others.

I don't have any proof of this in real pools (yet), but I believe that using a small amount of CYA in indoor pools, say 10-20 ppm, will significantly reduce the aforementioned problems. My wife experiences the degradation of swimsuits, skin and hair problems when using the community center indoor pool that are noticeable during even one winter season of use with 1-2 ppm FC and no CYA while no such problems occur in our outdoor pool with 3.5 ppm FC and 30 ppm CYA over 4 summers of use. What I don't know is what will happen (in an indoor pool with CYA) with Combined Chlorine over time. My hunch is that the production of CCs will be slowed down, especially those persistent CCs that I believe take a while to form in the first place which is why they are so resistant to "break" through simple addition of chlorine (i.e. the activation energy of formation is relatively high so it doesn't reverse or go forward very quickly). If the effective disinfecting chlorine (hypochlorous acid) concentration is lowered, then the formation of CCs may get slower as well. It doesn't eliminate the problem, but may make it manageable through normal dilution (water replacement) which should be done in any commercial pool over time anyway due to the buildup of many substances, including salt.

So I don't have good answers for you on solving this problem, but may have a way of reducing it in the future if you are willing to try it out. It may be that slowing the formation of CC will have the existing CC drop over time, especially with some dilution and air exchange. Of course, once one adds CYA to water, one cannot remove it except through dilution or through use of one of those designer MPS products that are exceptionally powerful (fast) oxidizers (essentially MPS with a cobalt catalyst), so if I'm wrong it's not easy to undo the "experiment". That is part of the reason no one has tried it (yet), but I'm still hopeful. By the way, at the other extreme, there are some indoor commercial (typically hotel) pools that use Trichlor feeders and have too much CYA. This produces other problems, mostly too slow a breakpoint of ammonia/urea which leads to very high monochloramine levels that can be irritating. So too much CYA is bad and no CYA is bad but a moderate amount is just right -- sounds like Goldilocks and porridge.

Richard
 
Wow, that really does make a lot of sense...point clearly taken.

Will adding CYA create a disinfection problem seeing that I'm running a commercial pool with a swim team in it everyday? I may be misguided on the strength of chlorine...

I've also heard of these non-cl shocks, but will they make my controllers go haywire?

Thanks a ton, you guys are quite impressive.
 
With CYA you will need somewhat higher FC levels than you do with no CYA at all. The instantaneous disinfection rate will be lower with the CYA, since the CYA will be "buffering" some of the chlorine. As the available chlorine gets used up the CYA will release the chlorine it has "buffered". Because there is more total FC, there will be a higher total disinfection ability that you would have had without CYA. At the same time, the negative effects on bathing suits and hair that high chlorine levels without CYA have will be dramatically reduced.

CYA will have an impact on the ORP controller. The ORP levels will read lower with CYA than without. The required increase in FC level will partially compensate for this, but you will need to re-evaluate what ORP level you are aiming for after making the switch. As long as the CYA level is kept reasonably low the ORP system will still function correctly. As the CYA level rises the ORP sensors become less precise. This effect is gradual and is not normally an issue with CYA levels around 20, but with CYA levels above 40 it can start to cause significant issues and somewhere over 50 the ORP system will no longer be effective.

Non-chlorine shock does cause significant problems for ORP controllers. MPS causes the ORP to read high even when chlorine is low. Since MPS is not a complete replacement for chlorine that can cause serious problems.
 
Also, keep in mind that outdoor public and commercial pools typically use CYA so it's not as if the disinfection rate will be any different than in such pools. If you use a smaller amount of CYA in the 10-20 ppm range and you keep the FC at 3 ppm or more, then the disinfection rate should be higher than in most outdoor pools. Fortunately, it takes a very small amount of chlorine to kill most bacteria. The reason for the higher FC levels is to have a "reserve" of chlorine and using CYA lets you have such a reserve while not "over-chlorinating" in terms of too high a hypochlorous acid strength. Technically, CYA is a hypochlorous acid buffer.

So you could start with something small like 10 ppm CYA at 3 ppm FC that you now target and this is technically equivalent in disinfecting chlorine to 0.3 ppm FC with no CYA, but you'll be able to maintain this disinfecting chlorine level easily without it "running out" even with local demand since the chlorine will get released from CYA relatively quickly (in seconds, as it does in the FC tests themselves). Right now, your indoor pool has at least 10 times more disinfecting chlorine than it needs to have.

As for ORP readings, every controller is different, but your ORP reading with 3 ppm FC and no CYA (and temp of 82F and pH of 7.4) is probably in the range of 795 to 808 mV (first number is with Chemtrol; second is with Oakton). With 3 ppm FC and 10 ppm CYA, the ORP reading will be between 703 and 737 mV which is still far higher than the 650 mV minimum usually desired in public/commercial pools.

If you do use MPS to shock, as Jason points out it will raise the ORP even though it's not a disinfectant (at least not fast-acting) and does so because it is an oxidizer with roughly the same strength as chlorine. Fortunately, it tends to break down quickly even after it's run out of things to oxidize so after a day or two the ORP level should be back to measuring (roughly) the hypochlorous acid chlorine level. Also, MPS supposedly registers as CC (though see below where it registered as FC in one person's test) though this interference can be eliminated using the Taylor K-2041 assuming you are using a Taylor K-2006 or similar FAS-DPD chlorine test kit.

I don't want to discourage you or anything, but in the interest of full disclosure you can look at this thread where we couldn't convince someone with a similar issue to try the CYA since his techs didn't want to try it out, not even in one pool. There is also this thread where a homeowner's indoor pool CCs didn't even go away in bucket tests under UV lamps (though FC did) nor high levels of shocking with chlorine or MPS (which interestingly measured as FC instead of CC). So it seems to me to be important to prevent such persistent CCs from forming in the first place. You can certainly do some experimentation of trying to get rid of CCs by using bucket tests, but you can't really test the prevention of CC formation since that requires bather loads in a lower disinfecting chlorine environment (i.e. a pool with CYA in it).

Richard
 
i cant offer any real help , s ( i cant even test my out door pool right, lol)

but i have to ask, sorry if this wastes your time, but is this a commercial pool, or your private pool. I thought my pool was big. LOL.

you ( as you have already seen) are getting the best pool help i have ever seen :wink:

also if it is commercial, does that mean you have to 24/7 circulate, and if you do, does that not cause airation, raising the PH. . or are the returns on the bottom like most indoor pools, not rippling the water?

sorry im a geek for in that "how many returns and how big of pump" does your pool have kind of thing. LOL :roll: :lol: :eek:
 
a few more points to consider...
You mentioned that you have problems keeping the pH down when you shock. How are you testing pH? If you are using a phenol red test then you are probably seeing interference from high sanitizer levels and not an actual rise in pH . Phenol red will convert to chlorphenol red in the presence of high chlorine levels. Chlorphenol red will have exactly the same color changes as phenol red but they occur at a much lower pH (4.6 to 6.8 ). If you are using a pH meter (assuming it is kept properly calibrated and the electrode is kept moist) then your readings are probably correct. However, that is only half the equation. Sodium hypochlorite can cause a slight pH rise but as it is used up and converted to chloride ions and sodium ions the reaction is acidic and pH will then fall. I would not worry too much about the actual or perceived rise in pH when shocking in actual practice.

Also, in a pool with persistant CC it might be useful to test for nitrates. Ideally nitrates should be 0 ppm but if they are not this could be a contributing factor to persistant CC. If nitrates are present the souce of them needs to be identified since the only way to get rid of them is by dilution with water that is nitrate free. Sometimes extremely high chlorine levels (50-100 ppm) can reduce or eliminate nitrates.

MPS, sodium percarbonate, and "designer oxidizers" will cause ORP to read high but they are only oxidizers and not sanitizers so ORP will not be a good indicator of sanitizing ability if these are used. Likewise, they will show up as CC unless a special reagent is used to remove the interference with DPD or FAS-DPD testing. To the best of my knowledge they do not form Wurster bases (red color) with DPD so they should not interfere with a FC test so the one case that was sited above I suspect was testing error.
 
Firstly thanks for all the replies...

I run an indoor natatorium with 3 bodies...main, training and spa.

24/7 circulation is required on all of them, with the main running at ~500 GPM open vacuum, training at ~150 GPM pressure and spa at ~100 GPM pressure. (All DE filters)

I have skimmer returns about a foot-foot.5 under the water in all bodies, so aeration isnt a huge factor. I run CO2 PH control on the two smaller bodies and acid on the main pool. (to control alk)


This CYA seems like a great idea...I may find the courage to try it.
From what I understand about the correlation with MPS and ORP...I can wait it out and ORP levels will return to normal?


Thanks so much guys...
 
Yes, after you use MPS it will slowly dissipate. It might go away quickly but more likely will hang around for several days to a week. Once the MPS dissipates the ORP readings will return to normal. While the MPS is around you will need to depend on manual water testing to maintain the correct FC level.
 

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MPS oxidizes ammonia and organics at a much faster rate than chlorine so if both are in the water it's the MPS that will get used up first. So I figure that in a pool with some bather load, the MPS will drop pretty quickly. But it will muck up your ORP and automated dosing control until its level drops. I may be wrong about it dissipating quickly if there is no demand, but in your pools that have usage, I wouldn't expect it to last very long once people get back into the pool.

To avoid wasting time with MPS in the big pool, I suggest you just do a bucket test to see if you can rid the CCs using MPS. If it can't get rid of them in a bucket, it's not going to get rid of them in a larger body of water. Besides, it's fun dosing a "pinch" to get the right amount into a bucket :? To find out if you've really eliminated your CCs, however, you'll have to get the MPS interference remover since you won't be able to distinguish between real CC and MPS-influenced CC without such remover.

Richard
 
According to the seminars I've attended and the literature that I have read and the questions I have asked MPS tends to stay in reserve in the water for close to a week when dosed at the recommened levels which is why it is not used with ORP controllers.
For MPS to be effective at oxidizeing organics BEFORE they form CC a reserve must be in the water at all times, unlike shocking with chlorine, which is done on an "as needed" basis.
 
OK, I stand corrected. It's inconsistent with their claims about it being a faster oxidizer than chlorine (for ammonia and organics that have not yet combined with chlorine) so something is amiss. They'd have to have one heck of a residual if it's only added once a week. Another one of those mysteries we may sort out with experiment on this forum. :-D
 
chem geek said:
OK, I stand corrected. It's inconsistent with their claims about it being a faster oxidizer than chlorine so something is amiss. Another one of those mysteries we may sort out with experiment on this forum. :-D
Click to expand...

Actually, DuPont explicitly states that Oxone (MPS) is NOT a better oxidizer than chlorine!

"4. Is Oxone® a better oxidizer than chlorine?
No, but it is more appropriate for pools and spas. Products containing Oxone® give you the positive benefits of oxidation without the drawbacks of high chlorine doses: reducing sanitizer efficiency, not eliminating all wastes and forming chloramines that produce unpleasant odors, irritate bathers' eyes and prevent you from using the pool for a lengthy period of time."


I take some of their claims with a grain of salt! :wink:

They also talk about "preventive oxidation" weekly on the oxone website.

"8. Does Oxone® reduce chloramines?
Products containing Oxone® prevent chloramines from forming by oxidizing contaminants. Regular oxidizing with Oxone® keeps contaminant levels to a minimum, so the water remains clear and sparkling, allowing you to enjoy longer periods of uninterrupted swim time."

Here is the link if you want to read the full text.
http://www.dupont.com/oxone/faq.html#oxone
 
I was getting my info from an E-mail exchange I had with Dupont. They said it was a selective oxidizer so actually oxidized some compounds that chlorine didn't (or didn't as well) and the whole idea was that it would oxidize those organics and ammonia before chlorine did thereby virtually eliminating disinfection by-products. I agree with you about questioning marketing claims, but the guys I communicated with were PhDs (a research associate). Nevertheless, the only way to know for sure, especially in environments with chlorine AND CYA, is to experiment and see what happens.

For example, the following are some responses from some queries I had:

Anecdotally, Oxone seems to have some efficacy at breaking down or
inhibiting biofilms. We have not yet developed good hard data, though, and
we certainly do not make any marketing claims on biofilm efficacy at this
point. Cobalt is a much more effective catalyst for MPS than is copper.
Co(II) generates sulfate and hydroxy radicals which are potent,
indiscriminate oxidizing agents. However, if a substrate is not
immediately available, non-productive decomposition of the AO results.

Uncatalyzed MPS is a strong, but kinetically-selective oxidizer. So it
should not be expected to oxidize all organic matter (unlike chromic acid
for example). MPS is effective at the oxidation of reduced sulfur and
nitrogen compounds along with epoxidation of olefins. Saturated
hydrocarbons are not oxidized by MPS. At the usual concentrations in pool
water, MPS does not react with CYA, so compatibility has never been an
issue in practice.
 
I think this link helps explain why it is said that MPS isn't a stronger oxidizer than chlorine. It's standard reduction potential is +1.44V compared to chlorine's +1.482V. However, this just gives the thermodynamic tendency and not the reaction rate. After all, oxygen with a lower reduction potential can oxidize organics as is evidenced by burning (or by use of some enzymes, though those are normally to be used with chlorine), but the rate is too slow at normal temperatures due to the high activation energy. MPS is selective in that it has a reasonably fast rate for certain kinds of oxidation and I think that's all that was being described in what I quoted from Dupont.

I've used MPS in my pool before and never noticed elevated CC after the first day. I'm sure that if I added more that I could end up with a residual at some point though I used a larger than normal dose.

This patent describes the use of persulfate to oxidize chloroform and it's enhanced with UV (so perhaps with sunlight). So while persulfate may not be good at oxidizing all Combined Chlorine, it looks like it is good at oxidizing chloroform (a trihalomethane). This is literally persulfate, S2O82-, not monopersulfate, SO52-, though a small amount of persulfate (about 3% as shown here) is found in most MPS products and is probably what irritates those with skin sensitivity (a guess on my part).

I found this interesting link showing some oxidation pathways of potassium monopersulfate (oxone, MPS). Isn't the Internet wonderful? I'm bookmarking this organic chemistry website. Oxidation of organics with ozone are shown here while oxidations with sodium hypochlorite are shown here. Unfortunately, not many reactions are listed and those that are have catalysts -- mostly because the site is oriented towards chemical synthesis (so what chemists would do in labs). Chlorine mostly does substitution reactions with nitrogen compounds (replacing an attached hydrogen with chlorine) and to a lesser extent alkenes (carbon double bonds) where it attaches chlorine to one carbon and hydroxyl to another though the link shows epoxidation (which is what MPS does where oxygen attaches to both carbons and is described more fully here though in the presence of ketones to form dioxiranes as an intermediate). A more practical description of ozone oxidation may be found here.

It is interesting to note that (like chlorine) MPS does not completely oxidize organics as it will tend to stop when there are only saturated carbon bonds (i.e. single bonds) left. The MPS will tend to make the organic compounds more soluble so that makes them less noticeable (i.e. they are no longer "films" or "scum lines" or refracted cloudy clumps). That is, it tends to hide organics, not really get rid of them with a few exceptions such as ammonia breakpoint to nitrogen. In some cases, it makes smaller more volatile organics and these can outgas.

The point is that if an MPS residual is supposed to be in the water so that it reacts with chemicals before chlorine gets a chance to, then having a bather load with ammonia/urea from sweat should use up that MPS residual unless it was quite large. 1 ppm FC of chlorine is equivalent to 5 ppm of MPS or put another way, one pound of MPS (product as the triple salt) in 10,000 gallons is equivalent to 2.4 ppm FC of chlorine (it's 12 ppm of MPS product). So if bather load creates enough demand to use up 2.4 ppm FC of chlorine, then that's enough to use up one pound of MPS in 10,000 gallons which is the normal recommended dose for residential pools. I figured that commercial pools easily use up more than 2.4 ppm FC in a day due solely to bather load (in an indoor pool).

Richard
 
I have a somewhat related situation. Our pools are all indoor pools no larger than 50K gallons. Most 25K gall.
We currently use Zodiac salt systems and run pumps 24/7, all but the 50K pool have sand filters using Zeosand.

The city of one of our pools is about to mandate a .2 maximum CC level which is nearly impossible seeing as how the fresh city water has a .6 or higher level. Since we teach babies/youngsters to swim our policy is 90 degree water, 90 degree pool room. To help reduce the cost of heating our owner stipulates on nights when the outside temp reaches 50 degrees we must keep our pools covered. They cover with strips of some sort of 6 foot wide roll of white foam like material, something that can't possibly breathe. We never cover on nights when we shock though.
I recently installed a small ozone injection type system to see if that helped the CC levels but so far, no joy. I have a theory this is due to the pool cover.....would anyone agree or are these ozone systems worthless?

I'm considering the MPS type of shocking after reading this thread but I feel this ozone unit should have helped somewhat.

Any opinions? I've only got a few months to solve this or we're cooked. :cry:

Thanks in Advance
 
The ozone system should help noticeably. Ozone systems have some disadvantages, but they do help with CC levels. Sometimes it is difficult to determine if the unit if functioning correctly. Have you checked to see that the bulb is not burned out and the system is correctly hooked up to the plumbing?

UV and ozone systems will both break down some of the FC in addition to the CC, which often mean more total chlorine usage. They break down FC but balance that by breaking down organics which saves chlorine, the net effect is often higher chlorine usage, though it can go either way. Ozone will also have a negative impact on air quality for indoor pools.

Really good air circulation helps to control some kinds of CC. Persistent CC problems have become more common in the last decade or so and many people attribute this to the reduced air circulation that has become common with more energy efficient buildings. However this has not been experimentally confirmed and so remains speculative.
 

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