pH chart compensation for CYA

[xDom]

The chart at the bottom of the pH TA relationship wiki is based of a CYA of 30 ppm.

PH TA Relationship - Further Reading

www.troublefreepool.com

How much different would this chart be with a higher CYA? in particular, 65 ppm.

 

[mgtfp]

What's important in this table is actually Carbonate Alkalinity (CA), not Total Alkalinity (TA).

You have roughly CA = TA - 1/3 CYA

The factor 1/3 is actually pH-dependant, but let's ignore that for the moment.

As the table is (for CYA 30), CA is therefore about 10 ppm lower than the TA value in the first column, the values would be:

Carbonate Alkalinity:
30
40
50
etc

To get a Carbonate Alkalinity of 30 ppm with CYA of 65ppm, you need a Total Alkalinity of about 52 to get

CA = 53 - 1/3 x 65 = 30

You therefore have to replace the first column with:

Total Alkalinity (for CYA 65):
53
63
73
etc

 

[mgtfp]

The pH dependency of the factor in front of the CYA concentration in the CA formula is:

Factor = 0.388 / (1+10^6.83-pH)

pH	Factor
6.8	0.19
7.0	0.23
7.2	0.37
7.4	0.31
7.5	0.32
7.6	0.33
7.8	0.35
8.0	0.36

 

[xDom]

OK, Thanks for that. So would a change in the TDS have much of an effect?

Where I'm going with this is I'm thinking my pH issue from the other thread is to do with me over reading the pH.
According to that chart a TA of 53 and a pH of 8.0 has a perfect CO2 equilibrium.
I tested my water tonight on a pH tester at work and it was saying it was about 0.3 lower than what I'm getting off my tests at home.
That value would also correspond to the chart

Maybe I'm somewhat colour-blind.

I notice you have an Apera 60, I'm considering one.
I'm sure the tester at work is an expensive bit of kit but if it's like most other things at my workplace, it's probably not calibrated.

At least if I have my own I can be confident in knowing its calibrated.

 

[JamesW]

y = 0.38772333÷(1+10^(6.88 – x)), x from 6 to 9 - 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

Borates and Adjusted Alkalinity.​

Adjusted TA = TA – (CYA X CYA C.F) – (Borate x Borate CF)

Borate C.F (correction factor) based on pH.

pH.......CF

7.2.....0.051

7.4.......0.0786

7.6......0.1248

7.8......0.1989

Cyanuric Acid correction factor based on pH.

pH........CF

7.0.......0.22

7.1.......0.24

7.2.......0.26

7.3.......0.28

7.4.......0.30

7.5.......0.32

7.6.......0.33

7.7.......0.34

7.8.......0.35

7.9.......0.36

For example, if the pH = 7.6, TA = 90, Borate = 50 and CYA = 70, the adjusted alkalinity is 90 - (70 x 0.33) – (50 x 0.1248) = 60.66.

 

[mgtfp]

OK, Thanks for that. So would a change in the TDS have much of an effect?

Where I'm going with this is I'm thinking my pH issue from the other thread is to do with me over reading the pH.
According to that chart a TA of 53 and a pH of 8.0 has a perfect CO2 equilibrium.
I tested my water tonight on a pH tester at work and it was saying it was about 0.3 lower than what I'm getting off my tests at home.
That value would also correspond to the chart

Maybe I'm somewhat colour-blind.

I notice you have an Apera 60, I'm considering one.
I'm sure the tester at work is an expensive bit of kit but if it's like most other things at my workplace, it's probably not calibrated.

At least if I have my own I can be confident in knowing its calibrated.

I wouldn't rely on that table too much, and not take it for granted that pH will never be higher than the equilibrium pH. There may be other processes at play that increase pH. Just temperature dropping would come with a pH rise. And it would take some time for pH to get back to the CO2 equilibrium by CO2 absorption.

I am very happy with my Apera. But it needs some looking after in order to trust it. I recommend always storing it in storage solution, and it requires regular calibration. If one is not willing to do that, or to pay for all the storage and calibration solutions, then the drop test is certainly the better option.

I like being able to test pH at higher FC levels, have more confidence in the higher pH regions, and see drift trends much earlier. But it's not everybody's cup of tea.

 

[xDom]

I wouldn't rely on that table too much, and not take it for granted that pH will never be higher than the equilibrium pH. There may be other processes at play that increase pH. Just temperature dropping would come with a pH rise. And it would take some time for pH to get back to the CO2 equilibrium by CO2 absorption.

I am very happy with my Apera. But it needs some looking after in order to trust it. I recommend always storing it in storage solution, and it requires regular calibration. If one is not willing to do that, or to pay for all the storage and calibration solutions, then the drop test is certainly the better option.

I like being able to test pH at higher FC levels, have more confidence in the higher pH regions, and see drift trends much earlier. But it's not everybody's cup of tea.

Do you replace the tip regularly? How often does this have to happen?

 

[mgtfp]

Do you replace the tip regularly? How often does this have to happen?

Replacing the tip is a bit of an issue, they don't seem to sell them in Australia. I wanted to replace the tip after about three years, meter was getting a bit sluggish. Still getting correct tests results, but readings took longer and longer to stabilise.

Because the Aussie Apera distributors didn't sell just the tip, I bought one via US Amazon. But that was a dudd, didn't stay calibrated. International return didn't sound appealing, so I bought a complete new meter.

 

[JamesW]

Borates and Adjusted Alkalinity.

Adjusted TA = TA – (CYA X CYA C.F) – (Borate x Borate CF)

Borate C.F (correction factor) based on pH.

pH.......CF

7.2.....0.051

7.4.......0.0786

7.6......0.1248

7.8......0.1989

y = 4.6289 ÷(1+10^(9.15 – x)), x from 7 to 8.5 - 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

 

[xDom]

Replacing the tip is a bit of an issue, they don't seem to sell them in Australia. I wanted to replace the tip after about three years, meter was getting a bit sluggish. Still getting correct tests results, but readings took longer and longer to stabilise.

Because the Aussie Apera distributors didn't sell just the tip, I bought one via US Amazon. But that was a dudd, didn't stay calibrated. International return didn't sound appealing, so I bought a complete new meter.

Do you know if there’s an expiration date on the calibration solutions?

 

[mgtfp]

Do you know if there’s an expiration date on the calibration solutions?

There usually is, but that applies to unopened bottles only. Once opened, they need to be used within a certain period. Usually more critical for high pH solution as they are susceptible to CO2 absorption which lowers pH.

 

[AUSpool]

OK, Thanks for that. So would a change in the TDS have much of an effect?

Where I'm going with this is I'm thinking my pH issue from the other thread is to do with me over reading the pH.
According to that chart a TA of 53 and a pH of 8.0 has a perfect CO2 equilibrium.
I tested my water tonight on a pH tester at work and it was saying it was about 0.3 lower than what I'm getting off my tests at home.
That value would also correspond to the chart

Maybe I'm somewhat colour-blind.

I notice you have an Apera 60, I'm considering one.
I'm sure the tester at work is an expensive bit of kit but if it's like most other things at my workplace, it's probably not calibrated.

At least if I have my own I can be confident in knowing its calibrated.

The sample pH will change in transit to your work. I would just use your home test results. What pH kit are you using?