CYA Conundrum

[Wobblerlorri]

I first mentioned this in the thread CYA Surprise, where I had been misreading my Pentair CYA test and actually had a CYA of 140. I decided to leave it alone and drain half when I closed for the winter.

Today we did the testing, and my monthly test of CYA came back at 60 using the TF-100 kit method. While this is pleasant news, it also begs the question: where did 80 ppm CYA go? Sure, we've had some rain, but not enough to overflow and replace almost half the pool volume! Did it break down? User error? Tomorrow I'm testing side by side using both kits.

We Shall See.I

BTW: how long do you let the mixed solution sit before filling the final tube? The Pentair test has you let it develop for 2 minutes before reading.

 

[mknauss]

The Pentair CYA test is fine, at lower values. But not above 60 ppm.

I mix my solution and then do the rest of the tests. Then go outside, in mid day bright sunshine, and do the CYA test.
Fill the vial to a line, say 80, lower the vial to your waist level and glance for the dot, you see it, add solution to the 70 line, glance, see it, repeat until you no longer see it with a glance. Then use the CYA value one step above the line you read. So if you stopped at 50, use 60 ppm CYA. After each reading, I pour the solution back into the bottle and do it again. Normally three times. Helps nail down the right level.
The vial is in logarithmic scale. So it is not viable to interpolate between the lines. Just use the whole numbers, such as 50, 40, 30, ....

 

[Wobblerlorri]

But where did 80 ppm CYA go? Did it break down in the 90+ degree weather we've been having? Did it overflow out of the pool and get refilled with rainwater? Hasn't rained that much, though, so I kinda doubt that...

Just curious.

 

[mknauss]

What I was trying to say with Pentair test, I doubt that was accurate.

 

[Wobblerlorri]

Yeah, that's why I'm testing them side by side tomorrow. Right now I'm not trusting any results unless I do them myself (hubby did the TF-100 test, for the first time, today).

 

[mknauss]

Once your CYA goes above 80 ppm or so, with any test, there is significant error.

I would believe the 60 ppm result far more than the 140 ppm result from earlier.