Seeking pH Calculation

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H

Hossy

Member
Mar 25, 2019
16
Carrollton, TX
I've been the proud owner of my first adult-life pool since the end of 2017. The pool is chlorine and about 12,000 gallons with spa attached. I quickly made friends with my local pool shop and have learned quite a bit. Last year, I bought an electronic pool test kit, which has been extremely helpful in getting the balance just right. My wife and I love the feeling of well-balanced water as it makes all the difference, especially for my wife whose skin can get easily irritated.

I'm a very analytical person and, as such, created my own spreadsheet in Excel for tracking my pool tests historically, but also calculating things like the Combined Chlorine (CCL), True Alkalinity (Alk), and Saturation Index (SI). I'm on this forum seeking knowledge for the next step in my spreadsheet: What To Do. I was reading a lot yesterday and one thing I came across was the JSPSI, which was a wealth of information. I now have very accurate calculations for adjusting True Alkalinity (Alk), both with sodium bicarbonate and muriatic acid. What is currently eluding me is the more complex calculation for pH. My end goal is to have my spreadsheet be my one-stop shop for all my water-balance needs instead of referencing vague tables or phone apps where I have to re-enter the information.

I'm wondering if anyone can help me or point me in the right direction for finding an accurate calculation (not a table) for the addition of muriatic acid (lower) and soda ash (raise). Any help would be greatly appreciated!
 
Welcome to TFP.

Sounds like you are looking to recreate PoolMath App or PoolMath Webpage

What test kit are you using?
 
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ajw22 said:
Welcome to TFP.

Sounds like you are looking to recreate PoolMath App or PoolMath Webpage

What test kit are you using?
Click to expand...

Thank you, ajw22! I was actually looking at PoolMath and I find that it's probably the most comprehensive app that I've come across so far. The one problem I keep running into is that no app/web site seems to allow me to provide my own MSDS data for my muriatic acid. I say this because the acid I get from the pool store is manufactured by FSTI. The solution is 33% with a specific gravity of 1.18. This is different than all the muriatic acid options available from any app/site I've found so far. Additionally, I like having all the recommendations in one place and on one screen. I'm not trying to compete with anyone, though. :) This is just for my personal use.

The test kit I'm using is the LaMotte ColorQ Pro 9 Plus.
 
Hossy said:
Thank you, ajw22! I was actually looking at PoolMath and I find that it's probably the most comprehensive app that I've come across so far. The one problem I keep running into is that no app/web site seems to allow me to provide my own MSDS data for my muriatic acid. I say this because the acid I get from the pool store is manufactured by FSTI. The solution is 33% with a specific gravity of 1.18. This is different than all the muriatic acid options available from any app/site I've found so far. Additionally, I like having all the recommendations in one place and on one screen. I'm not trying to compete with anyone, though. :) This is just for my personal use.

The test kit I'm using is the LaMotte ColorQ Pro 9 Plus.
Click to expand...

@Leebo @redth should be able to add FSTI MA to a future PoolMath app update.
 
Hossy said:
The test kit I'm using is the LaMotte ColorQ Pro 9 Plus.
Click to expand...

We like everyone to report there reading using the TF-100 or Taylor K-2006C (and yes the 'C' is important..) because it gives us a level playing field where we all have the same reference..

If you are going to hang around here I suggest you get the TF-100 Test Kits or K-2006C. And also please put details of your pool in your signature.

I don't know what the difference is between the 7 and the 9 but here are some threads about the LaMotte ColorQ:

LaMotte ColorQ Pro-7 digital water test kit. Is it okay to use?

Lamotte ColorQ Pro 7 - just how accurate ( especially T.A and C.H. Readings)

Note that people question the accuracy of the TA reading on the LaMotte which is where you are high. I would sure like to see you verify your TA using a Taylor test kit or the TF-100 since it is the prime suspect in your high CSI.
 
ajw22 said:
@Leebo @redth should be able to add FSTI MA to a future PoolMath app update.
Click to expand...
Hi @ajw22, That sounds great. I'm sure that will be handy, but I'm still looking to do these calculations myself. I find that I learn quite a bit more when I dig into the details.
Here's the link to the MSDS: https://leslies.msdss.com/MSDSDetail.aspx?did=c0c404bf-00a9-48b8-9a94-35fdb3d7e89c&ReturnURL=/MSDSSearch.aspx?fm=0&tb=0

ajw22 said:
We like everyone to report there reading using the TF-100 or Taylor K-2006C (and yes the 'C' is important..) because it gives us a level playing field where we all have the same reference..

If you are going to hang around here I suggest you get the TF-100 Test Kits or K-2006C. And also please put details of your pool in your signature.

I don't know what the difference is between the 7 and the 9 but here are some threads about the LaMotte ColorQ:

LaMotte ColorQ Pro-7 digital water test kit. Is it okay to use?

Lamotte ColorQ Pro 7 - just how accurate ( especially T.A and C.H. Readings)

Note that people question the accuracy of the TA reading on the LaMotte which is where you are high. I would sure like to see you verify your TA using a Taylor test kit or the TF-100 since it is the prime suspect in your high CSI.
Click to expand...
I'm actually not having a high TA problem. Right now, mine is low so I'm raising it first. As far as I know, the 7 vs 9 refers to the number of tests the unit can do. I can do:
  1. Free Chlorine (FCL/FC)
  2. Total Chlorine (TCL)
  3. Bromine (Br)
  4. pH
  5. Total Alkalinity (ALY/TA)
  6. Calcium Hardness (CH)
  7. Cyanuric Acid (CYA)
  8. Copper (COP)
  9. Iron (Ir)
ColorQ PRO 9 Plus - 2067 - Pool and Spa - LaMotte

I have found that the TA reading is in line with my local pool shop and they use a Taylor test kit, although I'm not sure of the model.

EDIT: I'm actually planning on going to Leslie's today after work to double-check the reading from my meter since I'm just now starting to use it again for the season. I'll let you know if I find a problem.
 
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Sorry, I got you confused with another thread that had high TA.

We do not give much credibility with pool store testing, especially Leslies. If you are going to be seeking water chemistry advice here you will need to provide your own test kit results.
 
ajw22 said:
Sorry, I got you confused with another thread that had high TA.

We do not give much credibility with pool store testing, especially Leslies. If you are going to be seeking water chemistry advice here you will need to provide your own test kit results.
Click to expand...
I will keep that in mind, thank you. I agree. That's why I wanted to get my own tester and why I opted for one with a colorimeter vs visual color matching as it's more accurate.

In the meantime, can you assist or point me in the right direction as far as finding the calculation or rain dance for determining the amount of muriatic acid/soda ash to adjust pH?
 
Hossy said:
I will keep that in mind, thank you. I agree. That's why I wanted to get my own tester and why I opted for one with a colorimeter vs visual color matching as it's more accurate.
Click to expand...

The only test that we use that relies on visual color matching is the pH test. And some folks use pH meters for more accuracy. All other tests use drops and a color change that is extremely accurate and the gold standard for testing.

Hossy said:
In the meantime, can you assist or point me in the right direction as far as finding the calculation or rain dance for determining the amount of muriatic acid/soda ash to adjust pH?
Click to expand...

I don't know the precise calculations.. I have been happy to rely on PoolMath.

Unless others comment here I suggest you use the search function or browse through the The Deep End... where more technical discussion have happened. Or if you can read HTML code the PoolMath page is standalone and does the calculation.
 
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There is no simplified method or equation for calculating pH in a multi-component buffered solution. There are chemistry software programs that do that, but they typically make the weak ionic strength assumption and then do some basic algebra. Unfortunately, pool water has very high ionic strength and so that must be factored into the analysis. Also, pool water can have multiple species buffering the pH (carbonates, cyanurates and borates) which turns any analytic solution into a multiple variable/multiple equation problem. If you'd like a look at a closed form analysis for the pH of a 4-component system (thus creating a quartic equation that needs a root solver and constraint equations), you can read this paper -

Calculation of the equilibrium pH in a multiple-buffered aqueous solution based on partitioning of proton buffering: a new predictive formula

Implementing that in a spreadsheet is well beyond the ability of Excel. @chem geek has (or used to have) a freely available spreadsheet that he created for doing advanced pool math. It's fairly complicated with a lot of embedded macros and VB code that you can not access without his permission and even he will tell you it is NOT for the novice user as the layout is very much his own way of thinking. It attempts to calculate pH through an iterative method and does a fairly decent job. See this link -

Richard Falk's Pool Equations Spreadsheet
 
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ajw22 said:
Unless others comment here I suggest you use the search function or browse through the The Deep End... where more technical discussion have happened. Or if you can read HTML code the PoolMath page is standalone and does the calculation.
Click to expand...
Thank you! I will! Already started looking at the old PoolMath web page. I see the calculations. Now I'm going to attempt to understanding them and assign meaning to the constant values. :)

JoyfulNoise said:
There is no simplified method or equation for calculating pH in a multi-component buffered solution. There are chemistry software programs that do that, but they typically make the weak ionic strength assumption and then do some basic algebra. Unfortunately, pool water has very high ionic strength and so that must be factored into the analysis. Also, pool water can have multiple species buffering the pH (carbonates, cyanurates and borates) which turns any analytic solution into a multiple variable/multiple equation problem. If you'd like a look at a closed form analysis for the pH of a 4-component system (thus creating a quartic equation that needs a root solver and constraint equations), you can read this paper -

Calculation of the equilibrium pH in a multiple-buffered aqueous solution based on partitioning of proton buffering: a new predictive formula

Implementing that in a spreadsheet is well beyond the ability of Excel. @chem geek has (or used to have) a freely available spreadsheet that he created for doing advanced pool math. It's fairly complicated with a lot of embedded macros and VB code that you can not access without his permission and even he will tell you it is NOT for the novice user as the layout is very much his own way of thinking. It attempts to calculate pH through an iterative method and does a fairly decent job. See this link -

Richard Falk's Pool Equations Spreadsheet
Click to expand...
Hi JoyfulNoise! I know that pH has multiple variables going into it, which is why a simple algebraic expressions isn't available, but in the end I'm hoping to come up with some sort of formula even one that pulls from the other test measurements, like TA. I will definitely look into the spreadsheet you're referring to!

Flying Tivo said:
I guess it will be me to say that You are not enjoying your pool enough!:laughblue:

Felipe
Click to expand...
Haha! You're probably right, Felipe. But, I enjoy the science just as much!
 
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