Certified Pool Operator (CPO) training -- What is not taught

waste

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Re: Certified Pool Operator (CPO) training -- What is not ta

Thanks guys :!: :cool:

Richard, thanks! (and I'm glad you used a "p" instead of "l") Great use of the emoticons! (I've never seen you use so many :wink: :goodjob: :lol: )

Scott, it's now 5 years (at least in Maine) - I guess the patch they give you will wear out in that time :mrgreen:

Alex, you did the 50-50 course - shoot me a PM if you would like for me to tell you what my instructor told us to highlight ( I can tell you page # and paragraph - my typing ~ sucks or I'd quote the relevant info :| ) Also tell me if your instructor's initials are "R. F."

TFP ROCKS!!!!!!!!! I know I wouldn't have scored 100% without the knowledge I've 'picked up' here.
 

Ohm_Boy

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May 1, 2007
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Re: Certified Pool Operator (CPO) training -- What is not ta

Great going, Ted. Best memorization ever!! ;)
Just kidding, Ted. Proud you have your CPO now, and 100% is nothing to sneeze at.
 

Retep

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Mar 24, 2011
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Re: Certified Pool Operator (CPO) training -- What is not ta

Just stumbled on this thread. . .
I am a CPO myself - and -YES- there are so many things which are not being taught at this course.

The book ( 260 pages or so) certainly got lots of good information in there, however it is my opinion that some fundamental
facts are not being addressed or explained.

The most disturbing fact is that NSPF recommends a chlorine residual between 2-4 ppm. :shock:
(I mentioned this already in another thread)

In a nutshell : Swimming is being promoted as something good for your health. Chlorine
is still the best sanitizer in order to prevent RWI (Recreational Water Illness).
I do disagree with those high recommended residuals (2-4ppm) for the following reasons:
The higher chlorine levels are, the more by-products (DBP)of chlorination are created. Some of those are linked to cause cancer in humans.
A swimmer breathes just above the surface of the water . By inhaling this air the swimmer also inhales gases such as Chloroform
and Trichloramines. Depending how long and with which activity the swimmer is in the water the more his(her) body gets enriched with those gases , which are a by-product of chlorination.

In North America the concern seems to be keeping the water safe in terms of microbiological parameters , but not on the chemical/physical parameters.

Germany adopted in the late 70's a completely different approach. Why you may ask ?
Germans found out that a disproportional high amount of people who worked in a swimming pool environment (especially in indoor pools) had a much
higher rate on cancer then the average population. The government back then undertook some research and found out the culprit was due to high
concentrations of chlorine in the pool water ( back then it was also anywhere up to 2 ppm). New regulations and laws came into effect in the early 80's ( DIN 19643).
The aim was to prevent the formation of DBP while still maintaining microbiological safe water in order to protect the public from RWI.
The Industry was basically forced to come up with new water treatment techniques in order to satisfy the tough new regulations.
Free chlorine levels were set at 0.30 ppm min. and 0.60 ppm maximum. Combined Chlorine max. 0.20 ppm and also ( and that's very interesting)
THM (Trihalomethanes). The profession of real Pool Engineers was created - those engineers designed sophisticated filters, paid attention to filtration speeds, pool hydraulics, expansion tanks and so on.
Meanwhile more and more health agencies became involved to study the subject of proper water treatment in swimming pools. In short - it became a science in Germany.
Additional water treatment systems got on the market such as Ozone and UV . Some seemed promising but in most cases they also had their disadvantages. Ozone is basically no longer found in German Pools and UV is not being used in public Pools since it was proven that it leads to high THM's in chlorinated water. THM levels are regulated in German pools - the maximum is 20 ppb ( micrograms/ liter) !
So - while it showed promise in reducing Chloramines ( which it does) it created a far more dangerous compound - the formation of Chloroform.

Why don't we follow those strict guidelines after we know by now all those problems associated with (mostly public)
swimming pools ? I am puzzled that those facts are not mentioned in the CPO Handbook and the NSPF did not take a closer look at those
researches. Could it have to do with the fact that some chemical manufacturers as well as equipment manufacturers are involved with the NSPF ?
My guess is as good as yours, but it makes one wonder. . . .

Has any public pool their water tested on THM's or TOC (Total Organic Carbon) in the USA or Canada ? The answer is probably "No".
Recently I do see a trend though (at least in Canada) that pool operators are getting more aware of the facts and try to set their own standards.
I am certain that soon or later tougher standards are being set by local health authorities (States or Provinces). Many other European countries
orient themselves after the German DIN 19643 for good reason.

Here are some links that some of you might find of interest . None of those links were written by companies/manufacturers , but by health agencies / research institutes and government agencies.
Enjoy !

Analysis of Swimming Pool Water –
Assessment of Results According to German Regulations
http://www.lims.hu/media/furdokonf/Engl ... ger3_p.pdf

Dr. Benoit Levesque Study – published in “Environmental Health Perspectives” – Vol 102, Dec 1994 -> ( effect of chloroform in swimmers )
http://www.ncbi.nlm.nih.gov/pmc/article ... 8-0088.pdf

What’s in the Pool? A Comprehensive Identification of Disinfection By-products and Assessment of Mutagenicity of Chlorinated and Brominated Swimming Pool Water ->
http://www.ncbi.nlm.nih.gov/pmc/article ... 8-1523.pdf

Interview with Monona Rossol (Chemist/Hygienist)- interesting what she says about monopersulfate (shock treatment)
http://www.youtube.com/watch?v=YZbh9NbuoJU

Exposure to trichloramine and respiratory symptoms in indoor swimming pool workers
http://erj.ersjournals.com/content/29/4 ... id=ersjnls

Baby swimming and asthma->
http://www.umweltbundesamt.de/uba-info- ... ection.pdf

Also 2 studies about UV radiation for pool water :

European Journal of Hydrology October 2009 (first paragraph in French with English below)
http://www.water-quality-journal.org/in ... er/2009009

Institut national de recherché et de securité France ( augmentation THM par UV)-> Study done in France by the French National Research and Security Institute –mostly written in French with some engl.
http://www.inrs.fr/inrs-pub/inrs01.nsf/ ... nd2237.pdf

:cheers:
 

JasonLion

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Re: Certified Pool Operator (CPO) training -- What is not ta

The main issue with lower FC levels is that in high bather load conditions the FC level can fall dramatically in some local areas of the pool. When FC starts low, local consumption can use up all of the chlorine and allow subsequent bather to bather transfer of pathogens, until that local patch of water gets it FC level raised again. In Europe this problem seems to be ignored/down played just as the US is ignoring/down playing the problems with disinfection byproducts from the higher FC levels.
 

Retep

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Mar 24, 2011
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Re: Certified Pool Operator (CPO) training -- What is not ta

JasonLion said:
The main issue with lower FC levels is that in high bather load conditions the FC level can fall dramatically in some local areas of the pool. When FC starts low, local consumption can use up all of the chlorine and allow subsequent bather to bather transfer of pathogens, until that local patch of water gets it FC level raised again. In Europe this problem seems to be ignored/down played just as the US is ignoring/down playing the problems with disinfection byproducts from the higher FC levels.

The reason that we have issues with lower FC levels at higher bather load is the following :
All public pools use an automatic control system. This consists of 2 probes. One measures the pH and the other one the
ORP. The "derived" FC read-out on the control comes from the automatic controller which converts now ( for example)
the actual ORP ( let's assume 730mV) at a pH at 7.3. This would theoretically translate to about 0.8 ppm.
So - now there are no bathers in the pool - the ORP is fine and all of a sudden 100 people jump in consuming all of those
0.8ppm. Since ORP probes are very very slow in detecting / reacting to those sudden changes it is quite possible
that there is all of a sudden no active chlorine in the pool. After a while - of course- the probe yells "I need chlorine"
and the pump kicks in which feeds now ( let's say) sodium hypochlorite like mad.
Meanwhile those 100 people decide to get out of the pool. What happens is that by the time the water (now again chlorinated) reaches
the ORP probe we got probably 2ppm or more in the water. . .
I am aware that probably 80% of automatic controllers used in public pools use the ORP control.
A much better way is to use an automatic control unit which is Amperometric. Those are much faster and by setting them
(for example) at 0.80 ppm there always will be 0.80 ppm in the water . Naturally it is always important to have
good water turn over based on the bather load and having good pool hydraulics so there is no dead spot anywhere in the pool.

Unfortunately ( and I see this very often) Pool builders and even engineers for public swimming pools don't really pay attention or are not aware of the importance of placing the inlet jets (filtered water) at the proper place.
Again - in Germany a so called "Dye Test" has to be performed before a public pool is opened. Only by making such a test we can see that there are no dead spots anywhere in the pool.

So - for this reason you can be assured that the Germans are very well aware what's going on and there is no ignorance or downplay as you
suggested.
 

JasonLion

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Re: Certified Pool Operator (CPO) training -- What is not ta

Amperometric sensors and optimized circulation do not take care of the problems I am describing. It still takes a minimum of 10 to 15 minutes for the water to remix even with idea circulation and continuous chlorine dosing. That is more than enough time for local chlorine deficits to develop and person to person transmission to occur. In practice remixing times are often far far longer than that. Avoiding these problems at low FC levels requires extreme circulation systems.
 

chem geek

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Re: Certified Pool Operator (CPO) training -- What is not ta

Please read the first post in this thread including many of the links provided. They explain a lot of what you talk about where there are assumptions or information you have that are not correct.

Retep said:
The most disturbing fact is that NSPF recommends a chlorine residual between 2-4 ppm. :shock:
:
I do disagree with those high recommended residuals (2-4ppm) for the following reasons:
The higher chlorine levels are, the more by-products (DBP)of chlorination are created.
:
Though it is correct that the higher the active chlorine (hypochlorous acid) levels are the more disinfection by-products (DBPs) are created, what you are missing are two critical facts. First is that the active chlorine level is not the same as the FC level or even close to it when CYA is present. CYA lowers the active chlorine level by orders-of-magnitude. Second is that the rate of creation of DBPs is roughly proportional to the total organic demand including that of bather load. Residential pools typically have far, far lower bather loads than commercial/public pools. Also, indoor pools have far worse air circulation than outdoor pools and do not have the UV from sunlight that helps directly reduce some chloramines and also breaks down some chlorine into hydroxyl radicals that can further oxidation of otherwise slow-to-oxidize compounds (such as urea).

Retep said:
:
Germans found out that a disproportional high amount of people who worked in a swimming pool environment (especially in indoor pools) had a much
higher rate on cancer then the average population. The government back then undertook some research and found out the culprit was due to high
concentrations of chlorine in the pool water ( back then it was also anywhere up to 2 ppm). New regulations and laws came into effect in the early 80's ( DIN 19643).
The aim was to prevent the formation of DBP while still maintaining microbiological safe water in order to protect the public from RWI.
The Industry was basically forced to come up with new water treatment techniques in order to satisfy the tough new regulations.
Free chlorine levels were set at 0.30 ppm min. and 0.60 ppm maximum. Combined Chlorine max. 0.20 ppm and also ( and that's very interesting)
THM (Trihalomethanes).
:
Though the German DIN 19643 is laudable, it completely lacks an understanding of how CYA works and therefore they do not consider it for use in their standard. A pool with an FC that is 10% of the CYA level has roughly the same active chlorine (hypochlorous acid) concentration as a pool with 0.1 ppm FC with no CYA, so even lower than the low-end of the 19643 standard. However, it can be difficult to maintain 0.3 ppm FC everywhere in a pool due to localized chlorine demand. CYA is a hypochlorous acid buffer so one can have a higher FC level to provide plenty of chlorine to meet localized demand while keeping the active chlorine level low to slow down the creation of disinfection by-products. Furthermore, as I detail in this post I also linked to in the first post in this thread, having a lower active chlorine doesn't just slow the rate of creation of nitrogen trichloride creation, but the total amount as well. The tradeoff is having a higher monochloramine and dichloramine level until these intermediates are fully oxidized.

The best part of the German DIN 19643 standard is the use of coagulation/filtration to remove organic precursors since this is the primary problem in high bather-load pools. However, this is not usually a problem in residential pools that are typically low bather-load.

Retep said:
:
Ozone is basically no longer found in German Pools and UV is not being used in public Pools since it was proven that it leads to high THM's in chlorinated water. THM levels are regulated in German pools - the maximum is 20 ppb ( micrograms/ liter) !
DIN 19643-3 specifies ozonation. It is not true that ozone is no longer used, though it may be used less frequently (mostly because the GAC required for ozone stripping doesn't work as easily or at reasonable cost in a high-rate sand filter environment). UV is a different story.

Retep said:
Has any public pool their water tested on THM's or TOC (Total Organic Carbon) in the USA or Canada ? The answer is probably "No".
Recently I do see a trend though (at least in Canada) that pool operators are getting more aware of the facts and try to set their own standards.
I am certain that soon or later tougher standards are being set by local health authorities (States or Provinces). Many other European countries
orient themselves after the German DIN 19643 for good reason.
Testing for THMs or other DBPs other than Combined Chlorine (which may mostly be relatively innocuous choroureas) is not required in the U.S. (requirements are by state and sometimes county). Part of the reason is that it is very expensive to test. I've tested TTHM levels in my own pool (as an experiment) and it costs $130 for each test.

Retep said:
Here are some links that some of you might find of interest . None of those links were written by companies/manufacturers , but by health agencies / research institutes and government agencies.
:
I've seen most of these papers, but some others were new and interesting. There are many, many others I've reviewed as well.

The video was interesting. It should be noted that the most irritating component of non-chlorine shock isn't the potassium monopersulfate (aka potassium peroxymonosulfate), but rather a minor component called potassium persulfate (aka potassium peroxydisulfate). Though it's possible that people have a reaction to monopersulfate, it's more likely that the problem was the persulfate/peroxydisulfate.

This Erdinger paper I find to be more interesting because as shown in Figure 5, simply having skin exposed to chlorine increases the chloroform level at a rate of 1 µg/L in this particular "arm in chlorinated water" test. So having a low active chlorine level is key to reducing this because all the coagulation/filtration in the world isn't going to help for skin, though obviously it helps for chemicals that are shed from the both (dead skin, sweat and urine). As I noted above, I've been doing THM tests and find that the levels are much higher if taken near a bather -- something that needs to be taken into account when doing such measurements.

One big elephant in the room is that urea is by far the largest nitrogenous component of sweat and urine and yet there is very little focus on removing this compound from the water. It does not create THMs, but does create nitrogen trichloride and is otherwise slow-to-oxidize from chlorine.
 

Retep

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Mar 24, 2011
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Re: Certified Pool Operator (CPO) training -- What is not ta

JasonLion said:
Amperometric sensors and optimized circulation do not take care of the problems I am describing. It still takes a minimum of 10 to 15 minutes for the water to remix even with idea circulation and continuous chlorine dosing. That is more than enough time for local chlorine deficits to develop and person to person transmission to occur. In practice remixing times are often far far longer than that. Avoiding these problems at low FC levels requires extreme circulation systems.

You are right - sometimes it even takes longer for the water to reach the sample cell of the automatic control. Most commercial pools measure the
"sample point" after the filtration. Some others have it before it goes back into the filters / expansion tank.
If it is a well maintained pool with proper water treatment and filters it does not really make much of a difference.
On the public pools I take care of , I regulary compare measurements from the actual pool water (measurements from different locations from the pool water) as well as taking a sample from the same point which controls the automatic control.

Those measurements are being taken with a Photo spectrometer for Cl2 (free and Total), ClO2 , pH and a Turbidity meter.

Results from Saturday May 21st 1.30 pm:

From Pool : FC = 0.71 ppm ; TC = 0.83 ppm ; Clo2 = 0.12 ppm ; pH = 7.32 ; ORP = 770mV ; Turbidity = 0.09 NTU
From Sample cell ( same spot where amperometric controler is connected - after filtration):
FC = 0.66 ppm ; TC = 0.74 ppm ; ClO2 = 0.11 ppm ; pH = 7.34 ; ORP = 784 mV; Turbidity = 0.08 NTU

As you can see there is hardly any difference between those readings. The set point on the amperometric automatic control is set at 0.7 ppm .
By the time I took those tests there was already a total of about 1000 swimmers in the pool ( from 6 am to about 1.30 pm).

Tests done on this pool have shown THM's levels at 14 ppb and TOC of 0.95 mg/lt,
 

chem geek

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Re: Certified Pool Operator (CPO) training -- What is not ta

Retep said:
From Pool : FC = 0.71 ppm ; TC = 0.83 ppm ; Clo2 = 0.12 ppm ; pH = 7.32 ; ORP = 770mV ; Turbidity = 0.09 NTU
:
Tests done on this pool have shown THM's levels at 14 ppb and TOC of 0.95 mg/lt,
I don't know why you refer to absolute ORP levels as if they mean anything. As I show in this post ORP readings from different sensors on the same pool water at the same time vary by more than 100 mV in 23% of the pools. As noted in this post, even Clifford White's classic "The Handbook of Chlorination" had inconsistencies measuring the same water as do tables from different manufacturers even on standardized water. ORP sensors are affected by the hydrogen gas concentration in the water so are affected by saltwater chlorine generator systems that more highly saturate the water with such gas. ORP is useful for process control, but not in determining water quality except as a very rough guide. ORP does not measure kill times -- non-chlorine shock can measure high in ORP but doesn't kill as quickly as hypochlorous acid. ORP does not measure oxidation rates either -- thermodynamic possibilities are not the same as real reaction rates which are often selective. An amperometric or other hypochlorous acid sensor is a more accurate assessment of at least the true active chlorine (hypochlorous acid) level.

Where is the chlorine dioxide coming from? Are you using that as a supplemental form of oxidation? Is this an indoor pool?

Also, what are you doing to get the THMs low? Are you using coagulation/filtration methods as with DIN 19643? Where is this pool -- in Europe or in the U.S.?
 

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Retep

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Mar 24, 2011
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Re: Certified Pool Operator (CPO) training -- What is not ta

chem geek said:
Retep said:
From Pool : FC = 0.71 ppm ; TC = 0.83 ppm ; Clo2 = 0.12 ppm ; pH = 7.32 ; ORP = 770mV ; Turbidity = 0.09 NTU
:
Tests done on this pool have shown THM's levels at 14 ppb and TOC of 0.95 mg/lt,
I don't know why you refer to absolute ORP levels as if they mean anything. As I show in this post ORP readings from different sensors on the same pool water at the same time vary by more than 100 mV in 23% of the pools. ORP is useful for process control, but not in determining water quality except as a very rough guide. ORP does not measure kill times -- non-chlorine shock can measure high in ORP but doesn't kill as quickly as hypochlorous acid. ORP does not measure oxidation rates either -- thermodynamic possibilities are not the same as real reaction rates which are often selective. An amperometric or other hypochlorous acid sensor is a more accurate assessment of at least the true active chlorine level.

Where is the chlorine dioxide coming from? Are you using that as a supplemental form of oxidation? Is this an indoor pool?

Also, what are you doing to get the THMs low? Are you using coagulation/filtration methods as with DIN 19643? Where is this pool -- in Europe or in the U.S.?

I do believe that ORP readings are very important.

The chlorine dioxide is a supplemental form of oxidation and also a reason to have those low THM readings in addition of
flocculation/coagulation as you can see by those low numbers in turbidity readings.
Pool is an indoor pool located in Canada.
 

chem geek

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Re: Certified Pool Operator (CPO) training -- What is not ta

Retep said:
I do believe that ORP readings are very important.
Read my post again as I've added more info and links. Are you saying it's important beyond its use for process control? Why do you believe it can be used as an absolute measurement? On what basis are you making that claim (and yes, I've seen all the papers correlating ORP to kill times and are no better and in some cases worse than using calculated hypochlorous acid concentration or that measured by amperometric sensors)?

Because you are mixing chlorine dioxide in with the hypochorous acid, you get a mixed (combined) ORP measurement. Kill times for these two substances vary. In practice, your FC levels with no CYA are very safe, but my point was that if you wanted to further reduce disinfection by-products, and I mean those created on skin itself, then you want an even lower active chlorine (hypochlorous acid) level -- say, down to the equivalent of 0.2 ppm FC with no CYA which can be readily achieved with 4 ppm FC with 20 ppm CYA. Of course, you say you aren't allowed to use CYA in indoor pools and that is true in most of the U.S. as well for commercial/public pools. Why do you think that is? It doesn't make any sense if one understands the chemistry known since at least 1974 (again, read the first post which links to papers such as this one). CYA doesn't just protect chlorine from breakdown from sunlight, but significantly moderates chlorine's strength while acting as a chlorine buffer.

Also, next time you take a THM sample, do so with bathers in the water and do so near one of those bathers. Especially in outdoor pools where people are using sunscreens, you will likely find high THM levels. I'm seeing if I can figure out if it's mostly the sunscreen vs. the skin itself.

By the way, I am not at all disagreeing with using better coagulation/filtration practices in commercial/public pools to remove organic precursors as much as possible. I have also written about using chlorine dioxide, though usually in the context for getting rid of Crypto via overnight shocking rather than trying to use superchlorination. The danger with using chlorine dioxide in the presence of chlorine is the formation of chlorate, though at the low concentrations of both you are using that risk should be low. Has Canada approved the use of chlorine dioxide in pools? That is something that has yet to be done in the U.S. as no manufacturer is apparently willing to pony up the $1-2 million to pass EPA DIS/TSS-12 with chlorine dioxide and in particular for the expensive safety tests that are required for EPA registration of a new chemical or a chemical for a new use.
 

JasonLion

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Re: Certified Pool Operator (CPO) training -- What is not ta

There are many misleading reports about the usefulness of ORP out there, almost all paid for by companies that sell ORP automation systems. The first paper you quote was sponsored by Chemtrol, who sells ORP automation systems.

As you pointed out earlier, the Germans have already figured this out, which is why they are switching to amperometric sensors which measure HOCl directly, instead of ORP which is an unreliable proxy for the HOCl level.
 

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Re: Certified Pool Operator (CPO) training -- What is not ta

Congrats Ted! I always knew you were certifiable! :mrgreen:
 

waste

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Re: Certified Pool Operator (CPO) training -- What is not ta

Thanks, John :cheers:

I thought Richard and Retep's interchange was the end of this - and I certainly have enjoyed their discussion.

Re: my being certifiable - on pool matters, I've gotten a few and always aced them - my shrink ~20 years ago, after 3 months, told me that 'Yes, you have issues but your coping mechanisms are keeping you OK so I suggest we stop these sessions until your mechanisms are no longer working" (that's a clean bill of mental health to me :lol: ) And I finally found a hobby - coming here :whoot:
 

chem geek

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Re: Certified Pool Operator (CPO) training -- What is not ta

Retep said:
Jason responded about the first link (one of many from Chemtrol that I've read), but the second link (the one above) isn't saying that ORP is better than calculated hypochlorous acid concentration. It is saying that it is better than FC alone to which I say "Duh!". Seriously, I'm not saying ORP is completely useless. After all, I already linked to graphs that show clearly that it is more correlated to hypochlorous acid concentration than it is to FC. However, ACTUAL hypochlorous acid concentration is even better than ORP when chlorine is the disinfectant and such actual hypochorous acid concentration can be calculated knowing the FC, CYA, pH and temperature (with some minor dependency on ionic strength) though is very reasonably approximated at usual pool pH by being roughly proportional to the FC/CYA ratio (technical derivation of this is in this post which is again one of the links in the first post in this CPO thread).

The pools in the Minnesota study (your link above) not surprisingly showed lower ORP in the outdoor pools because CYA is used there and it showed lower ORP with higher CYA, lower FC, and higher pH. This is to be expected since these are the same parameters that determine the hypochlorous acid concentration. The study showed that having code compliance did not assure an ORP >= 650 mV and this is not surprising since the code allows for an FC as low as 1 ppm and a CYA as high as 100 ppm which has an ORP of roughly 611 mV on Chemtrol, 549 mV on Oakton, 411 mV on Aquarius and (if you believe their tables) 113 mV on Sensorex. This is why I wanted the APSP-11 standard to specify the FC/CYA ratio for min/max or target levels since it correlates much better with hypochlorous acid concentration. Specifying ORP sensors with an absolute standard level would be less likely to produce consistent disinfection rates than using an FC/CYA ratio standard. The real debate should be about this minimum active chlorine level. My proposal is for a somewhat higher standard for commercial/public pools than we propose on this forum for residential pools, namely an FC that is 20% of the CYA level roughly equivalent to 0.2 ppm FC with no CYA and roughly corresponds to 717 mV for Chemtrol, 682 mV for Oakton, 629 mV for Aquarius, and 510 mV for Sensorex (so who are you going to choose??? This is just one reason why an absolute ORP standard is ridiculous and these values are regression-based with rather huge error bars as I've mentioned earlier).

What I don't understand is that you have mentioned the financial interests of chemical companies as possible reasons for promoting higher FC levels in the U.S. than in Europe, but don't ascribe the same motivations to ORP manufacturers. I suggest looking at scientific peer-reviewed papers and even then looking at multiple ones in different areas which is what I have referenced (for this specific topic) in the "Chlorine/CYA Relationship" section in the first post of this thread along with checking consistency with actual field data and the sum total of many people's experiences (not opinions or hypothesis).

P.S. when I plug in your numbers of pH 7.32, FC 0.71 ppm and use 82ºF temperature, I get an ORP of 770 mV for the Chemtrol sensor which is exactly what you see. So it's nice to know that the regression models based on manufacturer info (or actual field data for the Oakton) do work. But the fact that the different sensors vary so wildly, not only in absolute value but in the mV change per doubling in hypochlorous acid concentration, just means "absolute ORP" has to be taken with a huge grain of salt. Your pool reading of 770 mV is lower than your sample cell reading of 784 mV in spite of the chlorine reading in the pool being higher and the pH being slightly lower. Though 14 mV doesn't sound like a lot, 22 mV represents a doubling of hypochlorous acid concentration for the Chemtrol so 14 mV would mean the difference between 0.7 ppm and 1.1 ppm. Though not a disaster, you can't possibly use ORP absolute settings and have to instead use a setpoint. It also throws into question whether the "650 mV" touted as being safe really means anything since it depends on the sensor used, on the amount of hydrogen gas dissolved in the water, whether it is adjusted for temperature or pH (since pH affects ORP directly and in addition to its effect on hypochlorous acid concentration), etc.
 

Retep

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Mar 24, 2011
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Re: Certified Pool Operator (CPO) training -- What is not ta

The discrepancy you describe on tests with different ORP equipment is probably due to the following:
Since it takes such a long time to get the "final" reading on ORP in the water I assume that the readings taken
with the portable ORP meters were not accurate. I've seen it over and over again in the field ( public pools) that pool operators
take a water sample and submerge the portable ORP meter in a cup filled with pool water. After 1-3 min they think they got their final reading.
Wrong ! It takes up to 60 min. to get the "final" reading. It will slowly creep up until it reaches the maximum.

I also just posted in the ORP thread and posted the complete link about the Minnesota study. On this link they also posted quite a few references
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2646482/
 

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Re: Certified Pool Operator (CPO) training -- What is not ta

Retep said:
take a water sample and submerge the portable ORP meter in a cup filled with pool water. After 1-3 min they think they got their final reading.
Wrong ! It takes up to 60 min. to get the "final" reading. It will slowly creep up until it reaches the maximum.
There is much more going on there than you seem to be aware of. The ORP reading of the water is actually changing over that hour and the "final" reading does not necessarily reflect the reading in the bulk pool water. You have two problems which work at cross purposes here. ORP readings do take a while to settle down. But at the same time, taking a water sample in a cup drastically changes the surface to volume ratio of the water, which causes various interactions with the atmosphere to proceed far more rapidly than they do in the pool. CO2, chlorine, and hydrogen all start to outgas far more quickly than they otherwise would, causing the ORP of the sample to change from what it is in the bulk pool water. Your "final" ORP reading will reflect some of the chemical changes caused by this outgassing, and thus not be representative of the bulk pool water.
 

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