pH not changing. Bad acid?

[sean.a.hyde]

I just opened my pool.
Before I added any chlorine, I measured my pH at 8.0 using both my electric meter and the color match drop test in the TF100 Kit.
I have most of a jug of 31% acid from last year
To get it down to 7.4, Pool Math said to add 3 cups of 31% acid, so I added approx 3/4 quart.
I let that mix in, and then added 10ppm of liquid chlorine.

As the sun was going down, I checked both levels.
Chlorine was showing 9.5ppm (CC = 0.5)
pH was still showing 8.0, so I added another 2 cups of acid.

This morning, I tested again.
Chlorine is still 10 (CC=0.5)
pH is STILL showing 8.0.

Something I'm missing? The acid still certainly has vapors that don't smell pleasant... though maybe it is not quite as noxious as it used to be? It definitely still made some bubbles on the cement, but I guess it could just be much weaker.

 

[duraleigh]

Acid doesn't go bad. Perhaps you were well above 8.0 when you started. Keeping adding the acid in increments (as you are) and it will come down.

 

[BowserB]

Question, Dave. Is the pH measure still accurate at chlorine at 9.5 and 10ppm?

 

[duraleigh]

. Is the pH measure still accurate at chlorine at 9.5 and 10ppm?

Yes, it is unaffected at that range and affected less than people think even up into the teens. Nevertheless, the accuracy starts to lessen when FC goes above 10 ppm so it's always good policy to test pH when FC is less than 10 ppm.

 

[setsailsoon]

When did you calibrate your electric pH meter last?

 

[JohnT]

What is your TA?

 

[sean.a.hyde]

When did you calibrate your electric pH meter last?

A couple days ago. That’s why I did the drop test too.

What is your TA?

I’ve measured it twice at 60.

 

[JohnT]

My guess is your pH is actually higher than 8. Just keep adding and testing once or twice a day until you see some movement.

 

[setsailsoon]

How old is your calibration fluid and what brand/model meter are you using, how old is it? Electric pH meters are not usually interfered with by high FC.

 

[sean.a.hyde]

How old is your calibration fluid and what brand/model meter are you using, how old is it? Electric pH meters are not usually interfered with by high FC.

Brand new out of the box.

 

[sean.a.hyde]

Another quart got me down to 7.5

 

[setsailsoon]

How old is your calibration fluid and what brand/model meter are you using, how old is it? Electric pH meters are not usually interfered with by high FC.

Could be you had a buffered solution in your pool at pH 8? @JoyfulNoise Matt, is this possible?

 

[setsailsoon]

Another quart got me down to 7.5

Congrats! Now, that's more like it!

 

[setsailsoon]

What brand meter and what is it reading? Did you calibrate it or use it out of the box?

 

[sean.a.hyde]

What brand meter and what is it reading? Did you calibrate it or use it out of the box?

Apera PH60. I calibrated it with the 7.0 solution it came with, but it was pretty spot on out of the box.