Pool Water Chemistry (Warning: Can Get Technical)

[chem geek]

ubalr1,

I'm sorry you now get the Solver error. I assume this only occurs when clicking on the "Calculate pH/TA" button, right? This has been reported as very flaky on a PC and I was able to reproduce the problem on a PC and it sometimes would work and then it wouldn't, so I don't think it's only the version change but something very strange with PC's solver getting a spreadsheet created on the Mac.

I plan to replace the use of Solver, but am going on vacation (to Canada) for 2-1/2 weeks. I'm taking my computer and one of the things I'll do during down time (on the train, for example) is work on the spreadsheet. Yes, I consider that fun (shows how geeky I am).

I don't have the earlier version myself anymore. As soon as I replace the Solver with my own iterative code, I'll post it and let everyone know by a post to this thread. Again, sorry you got "hooked" with a working version. It's pretty neat when it works, eh?

I just put up the latest version just in case that one works for you. You can download it and try it out.

Richard

[chem geek]

ubalr1 and others,

I just removed the Solver dependence and uploaded a new (modified) spreadsheet. Give it a try and let me know if it works. Unfortunately, it will still "think" that Solver is being used when you load the spreadsheet so it will give you two macro warnings and may require you to add the Solver Add-In, but it won't actually use the Solver itself (which was the main problem).

[EDIT] As of around 8/30/06 I removed the apparent reference link to Solver that made Excel think that Solver was used even if it wasn't. [END-EDIT]

Richard

[ubalr1]

ubalr1 and others,

I just removed the Solver dependence and uploaded a new (modified) spreadsheet. Give it a try and let me know if it works. Unfortunately, it will still "think" that Solver is being used when you load the spreadsheet so it will give you two macro warnings and may require you to add the Solver Add-In, but it won't actually use the Solver itself (which was the main problem).

Richard

Hope you had a fine vacation Richard.

The speadsheet is working fine for me now. I had to uncheck the Solver in "Add-Ins". Thanks.

Couple of questions:
1) Can I change the concentration of Sodium Hypo? You have 11.9% in there. I use the 6% bleach.
2) I don't know what my Total Sulfates or Total Borates are. Can I still get accurate results using the spreadsheet?

[chem geek]

Hope you had a fine vacation Richard.

The speadsheet is working fine for me now. I had to uncheck the Solver in "Add-Ins". Thanks.

Couple of questions:
1) Can I change the concentration of Sodium Hypo? You have 11.9% in there. I use the 6% bleach.
2) I don't know what my Total Sulfates or Total Borates are. Can I still get accurate results using the spreadsheet?

I finally figured out how to remove Excel's thinking that there were references to Solver (when there weren't any more) so will update the spreadsheet with that fixed soon [EDIT] just uploaded an update today 8/27/06 with the Solver references removed [END-EDIT] [EDIT] and again today 8/28/06 with further improvements listing different concentrations for bleach in a pull-down menu. [END-EDIT]

Yes, you can get accurate results without the Total Sulfates or Borates entered, unless you have intentionally added lots of Borates (say, more than 30 ppm). The sulfates are there in case one has very high sulfate water (> 100 ppm) in which case this starts to affect the calcium carbonate water balance.

Richard

[fcfrey]

Richard,
I've been following this thread for quite a while and am wondering what is the latest date (version) on your spreadsheet. I've downloaded it several times but I'm not sure I have the latest.

I have printed out all the charts and graphs so I can study them --- my old brain take awhile sometimes.

I really appreciate the time you have put into this.

[chem geek]

I've been following this thread for quite a while and am wondering what is the latest date (version) on your spreadsheet. I've downloaded it several times but I'm not sure I have the latest.

Whenever I upload a newer version of the spreadsheet, I update the date near the end of the first post in this thread (near where I have the link to the PoolEquations.zip file) as well as the date in the first line of the spreadsheet and currently it's at 9/12/06 though I've made some minor changes since but haven't uploaded them yet -- mostly relating to this confusion about Trade % vs. % Sodium Hypochlorite for liquid chlorine and bleach. [EDIT] I uploaded a new update 10/30/06, but check the end of the first post to see the date of the latest update. [END-EDIT]

Richard

[chem geek]

Responding to this post.

Brad,

You can first check the first post in this thread on this forum that I created to explore the relationship between CYA and FC (check out the link near the end of the post where I have analysis about ORP as well). There's a lot of info there, but I also list the original source document that determined the equilibrium constants between the chlorinated cyanurates, cyanuric acid (CYA) and hypochlorous acid (HOCl). These constants are also found in this EPA document. There is also this article written by Kent Williams for the Professional Pool Operators Assocation (PPOA), but several people have said that Kent had an agenda as he was promoting ORP sensors, but my independent spreadsheet calculations (the spreadsheet is also found at the end of my post linked above) show that his data was essentially correct. Finally, this research paper indicates that the chlorinated cyanurates do not have disinfecting capability and in fact actually lower the effectiveness of hypochlorous acid -- in other words, not only does CYA significantly lower hypochlorous acid concentration (i.e. chemical equilibrium), but that small remaining hypochlorous acid is less effective in the presence of chlorinated cyanurates (but this is probably something unique to cysts that get some sort of sensitization from the presence of the chlorinated cyanurates). If you look at the table on page 1160 of the paper (click on the button for that page on the link), you can see reductions of "titrable Cl2" which is FC and that for CYA levels that are about the same (in ppm units -- the table shows Cy as moles/liter x10^5) the HOCl level is cut down by over a factor of 5. The situation is far worse when CYA concentrations are much higher than chlorine concentrations. By the way, I ran some of the numbers in the table in my spreadsheet and there is some error -- for example, the table at pH 7, Cy 7.0, Cl 14 shows HOCl as 1.88 while I calculate 2.18, but that's not a terrible error (though I wonder if the older equilibrium constants are off a small amount or if this paper's methodology is off or different...at any rate, it's not as if there is anything terribly wrong).

I am most proud of the fact that my results from theory match what Ben had discovered through observation in creating his Best Guess CYA Chart which I compare with calculated hypochlorous acid concentrations in a link in my post. If the calculations weren't borne out in the real world, they would be pretty worthless. The correlation with Ben's chart is pretty amazing for the Min/Max levels, above about 30 ppm, and the difference below 30 ppm is mostly due to Ben requiring minimum levels of chlorine so you won't run out, not just for disinfection. The shock levels don't track as well, but recent experience with nasty mustard/yellow algae on this forum has borne out the theory as well (some day, Ben's chart may be adjusted, but we'll need more validation before that -- and besides, it's his chart and his forum).

The bottom line is that the chemistry involved has been known for a long time and though a bit complex, it isn't quantum physics. I was able to do an accurate calculation in a spreadsheet. It is also possible to approximate the effects just looking at dominant species and only 2 of the 9 chemical equations (6 of which are independent). From my contact with various manufacturers, I would say that at least some are aware of these effects (one had done a spreadsheet themselves in order to create some of the data for the EPA link above), but that this information does not get out to the industry as a whole, probably for economic reasons. If people truly understood the relationship of CYA and FC to disinfection/oxidation, they would not use Trichlor as their sole source of chlorine (unless they backwash or drain/refill frequently) nor Dichlor as a frequent source in a spa. If people used chlorinating liquid or bleach (or an SWG) and did so properly so as not to get algae, then who would buy the expensive premium products (Trichlor, Dichlor, algaecide, clarifiers, flocculants, degreasers, stain removers)?

As for your 42 ppm FC example that was without CYA, that's a whole heck of a lot of chlorine so there is no wonder that corrosion occurred. By the way, for your indoor pool installations with no CYA, what is the typical FC level? Also, how do you shock the pool to rid combined chlorine (CC) and do you find that CC buildup to be a problem? Or do you use a weekly maintenance dose of non-chlorine shock (potassium monopersulfate, KMPS)? Since the only reports of people getting sick from pools is from indoor pools (presumably without CYA) with asthma and other repiratory ills from competitive swimmers and small children, I propose actually using some CYA (10-20 ppm) in indoor pools to significantly cut down HOCl levels since that would cut down the rate of production of disinfection by-products (DPBs). Also, using KMPS would eliminate such DPBs by avoiding chlorinated organics altogether. Radical ideas, but I don't think anyone has tried them to prevent the reported problems. (I know I'm getting off the topic of corrosion and if we get into this further, we should start a separate thread or go offline).

Richard