Error in Further Reading?

[TishTash]

In regards to CSI/LSI within the following:

CSI and LSI - Further Reading

www.troublefreepool.com

it states this:

“The results can be summarized as follows: […]

• at a given initial alkalinity and SI, the extent of precipitation decreases with increasing pH”

It’s fairly intuitive to follow that increasing alkalinity increases SI, as does cyanuric acid, boric acid, and TDS. My confusion is the part that states “the extent of (calcium) precipitation decreases with increasing pH.” I’m pretty sure that should be “precipitation increases with increasing pH,” especially since later the article states:

“The … equation is: SI = pH + Log[Hard] + Log[Alk] + TC + C”

Am I reading something incorrectly?

 

[PoolStored]

https://www.poolhelp.com/wp-content/uploads/2024/09/JSPSI_V3N1_pp18-23.pdf

 

[JamesW]

The results can be summarized as follows:

a) At a given initial pH and alkalinity, the extent of precipitation increases with increasing SI,

b) At a given initial pH and SI, the extent of precipitation increases with increasing alkalinity,

c) At a given initial alkalinity and SI, the extent of precipitation decreases with increasing pH, and

d) At a given initial pH, SI, and carbonate alkalinity, the extent of precipitation increases with increasing cyanuric acid concentration due to increased buffer intensity.

C and D do not make sense to me.

The extent of precipitation should increase with increasing pH.

The extent of precipitation of calcium carbonate should decrease with increasing cyanuric acid concentration because the cyanurate alkalinity replaces the carbonate alkalinity lowering the carbonate alkalinity.

Added CYA also reduces the pH, which lowers the rate of calcium carbonate precipitation.

 

[PoolStored]

C:




D:

 

[JamesW]

Still not buying it.

 

[ajw22]

Still not buying it.

Publish your own peer reviewed paper and we will quote and cite it.

 

[JamesW]

The amount of carbonate (CO₃^2-) increases as the pH increases.

So, the amount of calcium carbonate that precipitates should increase since the amount of carbonate (CO₃^2-) increases.

The Ksp formula for calcium carbonate (CaCO3) is: Ksp = [Ca2+][CO3^2-]; where [Ca2+] represents the molar concentration of calcium ions and [CO3^2-] represents the molar concentration of carbonate ions in solution at equilibrium.

graph y = 100/((10^(10.3-x)) + 1) and y = 100 - (100/((10^(10.3-x)) + 1)), x from 8.3 to 12.3 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[JamesW]

 

[JamesW]

The data show that CaCO, precipitation increases with increasing alkalinity at a given SI and decreases with increasing pH.

The change in precipitation with alkalinity and pH is due to a change in buffer intensity which varies directly with alkalinity and inversely with pH, in agreement with calcium carbonate precipitation potential (CCPP) theory (Wojtowicz 1996).

What is "Buffer Intensity"?

 

[JamesW]

Publish your own peer reviewed paper and we will quote and cite it.

First of all, I have no peers.

Second, what peers reviewed the referenced document?

 

[ajw22]

First of all, I have no peers.

I do agree you are 1 of 1.

Guess you will have to create some to be reviewed.

May be what AI is for.

Second, what peers reviewed the referenced document?

Question for the Journal of the Swimming Pool and Spa Industry.

 

[JamesW]

At a pH of 7.6, you have 99.8% bicarbonate and 0.2% carbonate.

At a pH of 8.2, you have 99.2% bicarbonate and 0.8% carbonate.

The precipitation of calcium carbonate depends on the concentrations of calcium and carbonate.

The amount of calcium ion stays constant and the amount of carbonate ion is increased by 4 times.

4Ca²⁺ + CO₃^2- --> 3Ca²⁺ + CaCO₃ (pH = 7.6).

4Ca²⁺ + 4CO₃^2- --> 4CaCO₃ (pH = 8.2).

graph y = 100/((10^(10.3-x)) + 1), x from 7 to 8.4 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

998HCO₃^- --> 2H⁺ + 2CO₃^2- (pH = 7.6).

pH.....Percentage that is carbonate.

7.0.........0.05
7.6.........0.20
7.9.........0.40
8.2.........0.80
8.3.........1.0

 

[JamesW]

To make the CSI equal for different pH levels, you need about 4 times the amount of calcium to compensate for the 4 times difference in carbonate.

So, you are comparing a calcium of maybe 240 vs. 1,000 ppm, which is not a fair comparison.

Effect of pH and Alkalinity on Precipitation of CaCO, -

The total dissolved solids was adjusted to 3000 ppm with NaCl.

Hardness was adjusted with calcium chloride to provide the required saturation indexes.

Ten ml of a 0.05% calcium carbonate slurry was added to each tank and stirred to homogeneously disperse the seed crystals.

 

[JamesW]

Also, if the pH starts at 7.6, it will naturally rise due to CO2 offgassing and the pH will be higher by the next day (Maybe 7.9).

If the pH starts at 8.2, the pH will not rise very much due to the very low level of CO2. The pH might rise to 8.3.

So, you are not making a fair comparison.

 

[JamesW]

All else being equal, rising pH increases the precipitation, or likelihood of precipitation, of calcium carbonate.

“The results can be summarized as follows: […]

• at a given initial alkalinity and SI, the extent of precipitation decreases with increasing pH”

I would remove this part from the article.

It’s fairly intuitive to follow that increasing alkalinity increases SI, as does cyanuric acid, boric acid, and TDS.

CYA, Boric Acid and TDS all lower the CSI.

 

[JamesW]

Cyanurate contributes to total alkalinity. Thus, it increases the CCPP for a given carbonate alkalinity.

In my opinion, this is also incorrect and should be removed.

 

[JamesW]

John A. Wojtowicz

John A. Wojtowicz of Goodyear, Arizona, formerly of Cheshire, Connecticut and Niagara Falls, New York passed away May 19, 2020. He was born on October 12, 1926 in Niagara Falls, New York to the lat…

www.courant.com

 

[JamesW]

 

[JamesW]

The solubility product constant (Ksp) for calcium carbonate (CaCO3) ranges from 3.36 x 10–9 to 6.0 x 10–9, depending on the form of the calcium carbonate.

pH = 7.78

(Calcium) 100 ppm CaCO3 = 0.10 grams per liter = 0.001 M Ca²⁺ (Moles per Liter of Calcium ions).

(TA) 100 ppm CaCO3 = 0.100 grams per liter.

0.001 M CaCO3= (0.5)X + Y

0.997(X + Y) = X (Moles per Liter Bicarbonate).

0.003(X + Y) = Y (Moles per Liter Carbonate).

X = 0.00198804, Y = 5.98205×10^-6

X = 0.00198804M HCO₃^2- (Bicarbonate Concentration Molarity). 1.988 X 10^-3M.

Y = 0.00000598205M (CO₃^2-). (Carbonate Concentration Molarity). 5.98 x 10^-6M.

(0.00000598205M)( 0.001 M) = 5.98 x 10^-9 (pKsp = 8.223).

10^-8.223 = 5.98 x 10^-9.

Molarity Carbonate X Molarity Calcium ions should equal the Ksp at a CSI of 0.0.

There are different Ksp/pKsp values for calcium carbonate and different pka values for the bicarbonate vs. carbonate.

There are factors for temperature and TDS that alter the equations.

So, you can get different numbers depending on the exact values you choose to use.

In any case, I would say that the most important thing is to track the CSI in PoolMath to make sure that the plaster is protected from etching and from scaling.

(Total Alkalinity/100086.9) = (0.5)X + Y

X = (1 - (1/(10^(10.3-pH) + 1)))(X + Y)

Y = (1/(10^(10.3- pH) + 1))(X + Y)

(Calcium hardness/100086.9)(Y) = Solubility Product

Solubility Product Calculator

https://claude.site/artifacts/7f211965-43ed-4857-b110-e19128c192c1

 

[AUSpool]

In regards to CSI/LSI within the following:

CSI and LSI - Further Reading

www.troublefreepool.com

it states this:

“The results can be summarized as follows: […]

• at a given initial alkalinity and SI, the extent of precipitation decreases with increasing pH”

It’s fairly intuitive to follow that increasing alkalinity increases SI, as does cyanuric acid, boric acid, and TDS. My confusion is the part that states “the extent of (calcium) precipitation decreases with increasing pH.” I’m pretty sure that should be “precipitation increases with increasing pH,” especially since later the article states:

“The … equation is: SI = pH + Log[Hard] + Log[Alk] + TC + C”

Am I reading something incorrectly?

This may not be explained very well but the summary as indicated there is a summary of that particular paper or article by Wojtowics and not to be confused as a summary of the CSI. It talks about other factors that start to explain some of the anomalies. While carbonate alkalinity is a primary indicator of CSI and increasing it will increase the CSI, increasing the alkalinity intensity will decrease it. But increasing alkalinity intensity will only decrease the CSI a little bit, alkalinity is still the primary factor.

From PoolMath increasing the pH, CH, and TA will all increase the CSI, increasing the CyA, Bor, salt will all decrease the CSI. A decrease in temp will decrease the CSI.