Pool Water Chemistry

[Titanium]

Richard,

if you could find out if the publisher still exists or got bought out and can get permission for me, that would be great.

I will certainly give it my best shot. Can you give me whatever information you have concerning the publishers name, city, address, telephone number, etc. that is in the "book" (sounds more like a conference symposium than anything)?

As for the APSP-11 developing standard, I gave rather extensive comments on it.

I probably missed it, but have you posted your APSP comments on TFP?

Titanium

 

[Rockcrawler]

Holy Smokes, I need a drink

 

[chem geek]

I will certainly give it my best shot. Can you give me whatever information you have concerning the publishers name, city, address, telephone number, etc. that is in the "book" (sounds more like a conference symposium than anything)?
:
I probably missed it, but have you posted your APSP comments on TFP?

Here is the info on the publisher from the book (and yes, it's a book, not just a conference summary -- many of the papers presented in the conference were consolidated into a hardcover book):

Ann Arbor Science Publishers, Inc.
P.O. Box 1425
Ann Arbor, MI 48106

(c) 1974
Library of Congress Catalog Card Number 73-82270
ISBN 0-250-40036-7

As for my APSP-11 comments, they include references to the proposed standard and this draft standard cannot be copied, redistributed or published so I'd rather not post my comments, but there wouldn't be any surprises there anyway.

Richard

 

[Titanium]

Richard,

As for my APSP-11 comments, they include reference to the proposed standard and this draft standard cannot be copied, redistributed or published so I'd rather not post my comments, but there wouldn't be any surprises there anyway.

I guess that begs the question of how you were able to obtain a copy of the draft.

Thanks for the publishers info. We shall see what we see.

Titanium

 

[Firefly2000]

Re: Oxidation-Reduction Potential (ORP) and HOCl

Oxidation-Reduction Potential (ORP) and HOCl

....It does seem that once an ORP sensor is calibrated then it does roughly track the HOCl concentration so is at least something to use in automated chlorine control systems....

Richard

Thanks for all the detailed info in this particular topic! Your efforts are appreciated. I could not claim that I fully understand the chemistry, but I can somewhat follow it.

I do have a particular interest in ORP. I have a pH-ORP based Acid and Chlorine dosing system (made by a vendor called "Rolachem"). How would you suggest that I calibrate the ORP sensor?

 

[JasonLion]

To "calibrate" an ORP sensor you get all of your levels to exactly where you want them using conventional testing and then note down the ORP reading. That ORP reading becomes your ORP target setting. This procedure needs to be repeated occasionally, to correct for any drift in the sensor or chemistry.

 

[Firefly2000]

So, you are saying that in the end it's not all that important what actual value the sensor reads, but that you try and maintain it at the same value once you know your water is good?

 

[JasonLion]

That is correct. ORP readings are affected by a number of factors other than chlorine. For the most part these other factors will only change slowly, so once you know what the offset is for your pool it is likely to stay at more or less the same place, that is to say that in the short run only the chlorine level will vary. But over time the other factors that affect the ORP reading can shift and you need to re-calibrate.

 

[chem geek]

I was able to track down the publisher where apparently Ann Arbor Science Publishers merged with Butterworth Publishers in 1983 and then became Butterworth/Heinemann, Elsevier Science and finally was just Elsevier. I contacted Elsevier to obtain reprint/publish/post rights but they said that "the title has gone out-of-print and the rights have reverted to the author". They did not know whether that meant the editor of the book, Rubin, or the authors of the paper/chapter, O'Brien, Morris and Butler.

So playing it safe I contacted as many as I could. I contacted Alan J. Rubin and received permission from him and I also contacted James N. Butler and received permission from him. J. Carrell Morris is believed to be deceased as he would be around 100 years old if he were alive. I was unable to locate Joseph(?) E. O'Brien.

So given that I have permission of the editor of the book as well as one of the authors of the chapter/paper, I believe I now have permission to make a PDF file of the chapter that I can then post online or E-mail to those who need it. I'll plan to do that when I get a chance.

Richard

 

[chem geek]

I've scanned the O'Brien paper into a searchable PDF that I link to from a web page here.

 

[Freelancer]

Richard I have found this to be are real interesting read.

I noticed that you have talked at length about how chlorine binds to CYA and that it's sanitizing potential is very low and is the reason why we must have higher chlorine levels at any given CYA level.

However I would be intruiged to know if this chlorine which is now bound to CYA is so poor at santizing how and when does it get released from the CYA to again become HOCI and as you say do it's thing.

Will CYA release HOCI when there is none present and thus the reason why we need slightly more to compensate for isocyanurates.

I have read pretty much every word in this post and apart from one snippet where you mention that when testing for FC the dye forces the CYA to release FC and thus is what we measure but you have talked very little about what really happens to the isocyanurates once they are formed. I have read O'Brian's paper and clearly isocyanurates do very little in the sanitization department so how do they actually contribute to the santization of the pools especially as you have mentioned that they are more like hypochlorite ion at best.

Finally going back to testing for FC. You said "the chlorine attached to CYA gets measured in the FC test because the chlorine gets released from the CYA quickly enough to replenish the chlorine that is consumed by the test (by reacting with dye)".

Then shortly after you made an EDIT "Free Chlorine (FC) does not measure active chlorine, but rather the chlorine reserve or reservoir that is mostly inactive".

Is not reservoir chlorine, FC and all chlorinated cyanurate species? Is this not a mixture of both the active and mostly inactive chlorines?

So if we are not measuring Active Chlorine are we only measuring isocyanurates? And if so how do we know how much HOCI we have in the water?

All of this has led me to one conclusion and that is if you are not dosing your pool daily then you certainly need some kind of automated chlorinator. There is such a fine line between a healthy and potentially unhealthy body of water.

 

[JasonLion]

One way to think about it is that at some specific CYA level there is always some fixed percentage of the HOCl that will be bound to CYA at any given time. If the unbound HOCl vanishes, additional HOCl will become unbound from CYA to restore the appropriate percentage bound as the system moves back into equilibrium. The movement back to equilibrium takes a moment, but not very long. When doing an FC test, HOCl is consumed, resulting in the release of any HOCl that is bound to CYA, until all of the HOCl is used up as part of the test procedure. Thus the FC test is measuring all of the HOCl, including that which was originally bound and that which started out unbound.

You can calculate the unbound HOCl level if you know the FC level and the CYA level.

 

[Freelancer]

Thanks for clarifying that Jason..

How do you calculate HOCI by knowing FC and CYA.

Also you said that HOCI gets used up during the FC test. Does that not mean that you actually have higher levels of HOCI than the test results show you?

 

[JasonLion]

FC getting used up in the test is simply part of the way the test works. HOCl reacts with the indicator dye to create the color you see when doing the test. The reaction with the dye "uses up" the chlorine, which prompts any bound chlorine to become unbound.

All of the FC tests are testing the FC level, which isn't exactly the same thing as the HOCl level. FC counts both HOCl and OCl-, which are also in equilibrium with each other at a ratio that depends on both the PH and the CYA levels. There is way more information about this in the early posts of this topic. For a typical pool, with levels in the normal ranges we recommend, FC and HOCl are related by the equations given in the first post of this topic

(HOCl as ppm Cl2) = (FC as ppm Cl2) / ( 2.7*(ppm CYA) - 4.9*(FC as ppm Cl2) + 5 )

 

[chem geek]

I've written about the concept of the reserve of chlorine and the speed at which chlorine gets released and the concept of why that speed doesn't matter in terms of the rate of killing pathogens in this post, this post and this post.

When I wrote "Free Chlorine (FC) does not measure active chlorine, but rather the chlorine reserve or reservoir that is mostly inactive", the "chlorine reserve or reservoir" includes both the chlorine bound to CYA as well as that which is unbound, namely HOCl and OCl^- which is why I said such reserve was mostly inactive since the chlorine bound to CYA has very little reactivity.

If you really want to know how much HOCl there is in the water, then you can use my spreadsheet to calculate it using primarily the FC, CYA and pH though other parameters also have a minor effect (there is also a temperature dependence, but I have that turned off at line 225 "Use Temp. Dependent Cl-CYA" in the spreadsheet since it came from Wojtowicz and not from a normal peer-reviewed journal). Roughly speaking, the HOCl level is proportional to the FC/CYA ratio and is very roughly half that ratio near a pH of 7.5 (Jason referred to a better formula I have for it, but even that is an approximation and only for a pH of 7.5 -- the spreadsheet does the accurate calculations).

Your pool does not become unhealthy when the chlorine gets below the minimum FC for your CYA level. It just becomes more likely to develop algae. Most bacteria and viruses are very easy to kill or inactivate and require very little chlorine to do so (some papers showing kill times are linked to in the "Chlorine / CYA Relationship" section in this post and there is also this CDC chart). The primary reason we have the minimum FC be higher is to prevent algae growth and to have faster bacteria and virus kill/inactivation rates to prevent person-to-person transmission of disease. It's not like all of a sudden the pool becomes unsanitary -- that pretty much won't happen unless the chlorine level is close to zero.

At the minimum FC/CYA ratios recommended on this forum for non-SWG pools, namely an FC that is around 7.5% of the CYA level, this is equivalent in HOCl concentration at a pH of 7.5 to a pool with an FC of 0.062 ppm with no CYA. Most heterotrophic bacteria have CT values of 0.04 for a 99% kill which means such a kill is done in 0.04/0.062 = 0.65 minutes or under 40 seconds. It takes at least 15 minutes for bacteria to double in population so this level of chlorine would kill bacteria faster than they can reproduce for any with a 50% CT of 0.93 which roughly corresponds to those listed with a 2-log 99% kill CT of around 6, a 99.9% CT of 9, a 99.99% CT of 12, etc. Pretty much everything in the CDC table is handled except for the bacteria Burkholderia pseudomallei, Vibrio cholerae (rugose not smooth strain), Yersinia enterocolitica. Though the 99.99% inactivation time for Poliovirus would be around 100 minutes, viruses do not reproduce outside their host. Similarly, the protozoan oocysts of Entamoeba histolytica and Giardia lamblia would take around 4 hours to inactivate 99% to 99.9%. The protozoan oocysts Toxoplasma gondii and Cryptosporidium parvum are essentially not inactivated by normal chlorine levels in any reasonable amount of time.

Richard

 

[Freelancer]

Thanks once again Jason..

Any chance of a working example of that formulae? It's the Cl2 bit that's throwing me...

 

[JasonLion]

"as ppm Cl2" is just the units that everyone uses for FC, ie just use the FC level straight from the test kit.

(FC as ppm Cl2) / ( 2.7*(ppm CYA) - 4.9*(FC as ppm Cl2) + 5 )

If FC is 5 and CYA is 50, HOCl is 5/(2.7*50-4.9*5+5) = 5/(135-24.5+5) = 5/115.5 = 0.043

 

[Freelancer]

Richard,

An excellent reply and having read the links which shed light even more so the pennies start to drop one by one. Also a really nice spreadsheet.. Going to have some fun getting aquainted with that..

Thanks once again.

 

[Freelancer]

Jason,

Excellent working example and I'm happy to now fully understand at least that formulae..

Having now read all yours and Richards posts on the subject I'm happy to say that finally I understand how bound and unbound chlorine works which is a great help indeed. Thank you both.

I can see now why a little CYA would most certainly benefit indoor pools.

 

[loop_pea]

Time to jump in at the deep end. After considerable contemplation, I think I understand the signficance of the HOCl ion and the fact that is is a proxy for sanitising power. But the relationship between CYA and FC still doesn't make sense completely to me.

Does this formula for working out HOCl above hold up at CYA levels over 100? The charts only go to 100. I know that pools aren't supposed to go over 100, but they can and do.

There's a paper called "Cyanurics, benefactor or bomb" which says that ORPs all seem to converge at the same level above about 70 ppm CYA. In other words at high CYA, you end up with about the same amount of ORP, regardless of your actual FC level.

Elsewhere you say that ORP is pretty unreliable, or at least that the ORP meters do not give consistent results, which isn't quite the same thing. ORP is affected by many things, but it is fair to say that in the same pool, with other factors held the same, then ORP is also thought to be related to sanitising power???

The convergence of the ORP suggests to me that the relatioship between FC and CYA may change at high levels of CYA. Is it possible that more HOCl will remain than expected from a simple linear equation (the ratio FC/CYA)?

TFP uses the ratio of FC/CYA to work out the shock levels. But if this relationship is breaking down at high CYA, then do you really need those incredibly high FC levels to shock high CYA pools?

Am I making sense? There are so many variables in these equations, that it's hard to see the trends. Apologies if this is a stupid question. This is fascinating stuff.