Low PH

[tikoh]

ok, I will recheck them both. I am pretty sure I'm testing both properly as I have watched the Taylor videos on youtube several times.

What has your TA historically been at? At very low pH (around 6ish), carbonic acid will actually show up as alkalinity. As the name would suggest, this is an acid and gives you low pH while also showing up as high alkalinity. There was an article by chem geek from a long time ago that explained this, but I can't seem to find it.

You can read about the carbonate system here: https://water.mecc.edu/courses/Env211/lesson7_4b.htm and if I find chemgeeks article relating it to pools I'll post it. Essentially, alkalinity is the capacity of a solution to resist a reduction in pH. At very high pH (like 11+), hydroxide ion [OH–] concentration is so high that it takes a significant amount of acid to neutralize enough of them before the pH drops. At very low pH, hydronium ion [H+] (which is actually acid) concentrations are very high, and as a result, a much higher concentration of acid is required to further lower the pH. Think about it this way, the more acidic you are, the harder it is to get more acidic. In between we mostly think of carbonates (CO3) as our alkalinity. At normal pool pH, it is bicarbonate (HCO3-). At around pH 6, that bicarbonate takes on a [H+] and becomes carbonic acid (H2CO3).

The TA test is a titration with a standard acid to a designated pH. The more drops it takes to get there, the more resistance the water sample has to a reduction in pH. When you're in a normal pool pH range, the acid eats up that HCO3-, drops the pH, and the color changes. However, when you're not in the normal pH range, the standard acid (sulfuric in most Taylor kits) doesn't react as readily with the carbonic acid and it actually takes more drops to get a change.

In any case, you have two options, and the best answer might be to do both... The first step is to aerate. Do it by whatever method works best for you, but do it like crazy. The other thing you can do is to use borax to raise pH while not significantly adding TA.

Of course, this is all assuming that your pH reading is correct, so I would also follow James' advice and try new reagents. You can get the phenol red pH test anywhere.

 

[JamesW]

At very low pH, hydronium ion [H+] (which is actually acid) concentrations are very high, and as a result, a much higher concentration of acid is required to further lower the pH. Think about it this way, the more acidic you are, the harder it is to get more acidic.

At very low pH (around 6ish), carbonic acid will actually show up as alkalinity.

Both of these statements are incorrect.

 

[shedlock22]

Show us a picture of your pH test.

 

[JamesW]

Leave the cover off for 24 hours to see what that does.

Double check the TA and pH with new reagents.

 

[tikoh]

Both of these statements are incorrect.

The first statement is most certainly true. pH is a logarithmic scale. A solution of pH of 4 has a H+ concentration 10 times that of a solution at pH 5 and a solution of pH of 3 has an H+ solution 10 times that of the pH 4 solution. Adding acid supplies those H+ ions. The pH 5 solution has an H+ ion concentration of 0.0001M and the pH 4 solution is 0.001M. To go from 5 to 4 you have to increase the concentration by 0.0009M. To make the same 1 pH jump from 4 to 3, you'd have to go from 0.001M to 0.01M which required a change of .009M which requires 10 times as much acid as the first change.

The second statement is a little more complicated, because we like to simplify our pool chemistry and pretend that the only variables are the ones that we measure. When you're doing a TA test, and you have high pH and high TA, and you drop that sulfuric acid in there, you can hear it sizzle. That sizzle is releasing CO2 in a chemical reaction just like baking soda and vinegar. When you're at a lower pH, less than 7, you're not getting that acid base reaction and instead, the carbonic acid in the solution can still act as a buffer.

 

[JamesW]

carbonic acid in the solution can still act as a buffer.

Carbonic acid is H₂CO₃.

To act as a buffer to pH drop, the carbonic acid would need to accept a hydrogen ion and become H₃CO₃⁺, which does not happen.

Carbonic acid can act as a buffer to pH rise, but not as a buffer to pH drop.

Carbonic acid or carbon dioxide is a form of Total Acidity, which measures the resistance to pH rise from added base.

 

[JamesW]

The first statement is most certainly true. pH is a logarithmic scale. A solution of pH of 4 has a H+ concentration 10 times that of a solution at pH 5 and a solution of pH of 3 has an H+ solution 10 times that of the pH 4 solution. Adding acid supplies those H+ ions. The pH 5 solution has an H+ ion concentration of 0.0001M and the pH 4 solution is 0.001M. To go from 5 to 4 you have to increase the concentration by 0.0009M. To make the same 1 pH jump from 4 to 3, you'd have to go from 0.001M to 0.01M which required a change of .009M which requires 10 times as much acid as the first change.

You are not accounting for the TA, which is what is being measured.

The lower the pH is, the lower the TA typically is.

In any case, we are not talking about lowering the pH in the 3 to 4 range, we are only lowering the pH when it is above 7.2 and the TA is the primary determinant of how much acid it takes to lower the pH.

 

[proavia]

How did you get a CYA result of 42?
If the CYA shows over 40 and less than 50, round up to 50.
The CYA scale is logarithmic, not linear.

For the FAS-DPD chlorine test, use a 10ml water sample instead of 25ml.
One rounded scoop of R-0870.
Each drop is 0.5ppm
Using the 10ml sample will save on reagents and is close enough for our purposes.

 

[JamesW]

The pH 5 solution has an H+ ion concentration of 0.0001M and the pH 4 solution is 0.001M.

pH............Moles per Liter

-1...............10

0..................1

1..................0.1

2.................0.01

3.................0.001

4.................0.0001

5.................0.00001

6.................0.000001

7............... 0.0000001

 

[JamesW]

When you're doing a TA test, and you have high pH and high TA, and you drop that sulfuric acid in there, you can hear it sizzle. That sizzle is releasing CO2 in a chemical reaction just like baking soda and vinegar.

I have never heard a "sizzle" but maybe I just have not noticed.

I will look for and listen for a "sizzle" when I do another TA test.

When you're at a lower pH, less than 7, you're not getting that acid base reaction and instead, the carbonic acid in the solution can still act as a buffer.

The sulfuric acid is reacting to the bicarbonate all the way down to a pH of 4.5, which is designated as the endpoint of the TA test.

This graph shows the percentage of carbonic acid (aqueous carbon dioxide) (Y-axis) vs. pH (X-axis).

 

[shedlock22]

Ok guys, appreciate the input but what does this all mean for my path forward? I have 8 # soda ash on hand. Also, my least favorite subject in high school was chemistry so this made my head spin

 

[JamesW]

Leave the cover off for 24 hours to see what that does.

Double check the TA and pH with new reagents.

 

[tikoh]

You are not accounting for the TA, which is what is being measured.

The lower the pH is, the lower the TA typically is.

In any case, we are not talking about lowering the pH in the 3 to 4 range, we are only lowering the pH when it is above 7.2 and the TA is the primary determinant of how much acid it takes to lower the pH.

I started to type a response that started with: "You're thinking like a pool guy...and we're not dealing with a pH above 7...and that H2CO3 will absolutely take that H+ and become H3CO3....everything in pool math is working under the assumption that the pH is greater than 7…"

But it's irrelevant. I'm a nerd. I studied chemistry in undergrad and worked in a limnology lab studying environmental chemistry in freshwater ecosystems while working on my masters. Prior to that I had worked for the village I grew up in maintaining their pools. I now work infection prevention in a hospital. All day I think about sanitization of water and surfaces. More importantly than being a nerd, I'm on the spectrum and I get really focused on nuances and technicalities. I'm obviously a TFP proponent, or I wouldn't be here. I believe that the base TFP protocol works for probably 95% of people 95% of the time as long as the basic parameters it’s assumptions are built on exist. My brain is wired to look for the outlier conditions, for the exceptions to the rules and chasing them. My personality is such that I will debate endlessly.

You’re obviously one of the most respected people on this forum and for good reason. I do not want to argue with you. I’d be happy to discuss more in the deep end if you’re into it, but if not, I’m good. I will come back to this thread if I come across Richard/chemgeeks article on the phenomenon of low pH high TA.

@shedlock22 , sorry for hijacking your thread

 

[shedlock22]

I started to type a response that started with: "You're thinking like a pool guy...and we're not dealing with a pH above 7...and that H2CO3 will absolutely take that H+ and become H3CO3....everything in pool math is working under the assumption that the pH is greater than 7…"

But it's irrelevant. I'm a nerd. I studied chemistry in undergrad and worked in a limnology lab studying environmental chemistry in freshwater ecosystems while working on my masters. Prior to that I had worked for the village I grew up in maintaining their pools. I now work infection prevention in a hospital. All day I think about sanitization of water and surfaces. More importantly than being a nerd, I'm on the spectrum and I get really focused on nuances and technicalities. I'm obviously a TFP proponent, or I wouldn't be here. I believe that the base TFP protocol works for probably 95% of people 95% of the time as long as the basic parameters it’s assumptions are built on exist. My brain is wired to look for the outlier conditions, for the exceptions to the rules and chasing them. My personality is such that I will debate endlessly.

You’re obviously one of the most respected people on this forum and for good reason. I do not want to argue with you. I’d be happy to discuss more in the deep end if you’re into it, but if not, I’m good. I will come back to this thread if I come across Richard/chemgeeks article on the phenomenon of low pH high TA.

@shedlock22 , sorry for hijacking your thread

Haha you’re good, appreciate the input