CYA Test - Am I doing it right?

Fronzizzle

Well-known member
Jun 29, 2017
85
Augusta Township, Michigan
Hello all,

I have a question about the CYA test. I know it's a little subjective, but I want to make sure I'm doing this correctly.

After mixing the solution (1/2 pool water, 1/2 reagent), I hold the tube with the black dot at waist level and add the solution until the dot disappears. My issue is that as I'm adding, I think the dot disappears but then I stop adding, and as I'm looking, I think it reappears. So I add a few more drops and repeat.

The last test I did, I was at 45 so I rounded to 50 and have been chlorinating my pool at that level. We haven't had any rain here, so I've had to add quite a bit of water over the last couple of weeks, and I noticed that my chlorine tests haven't been as consistent - I would bring it to 8 ppm and it would drop to 5 or 6 quickly, but then stay there. I did the OCLT and it was zero, the water is clear and I have 0 CC so I don't think there is any sort of algae or anything. I assumed my CYA was lower than 45, so I tested it and when the dot first disappears I'm somewhere around 35-40, but to get it to "stay disappeared", I'm closer to 25. So in the first instance, I need to chlorinate as if I'm 40 ppm and the second, I probably need to add a little stabilizer and assume I'm at 30 ppm.

I have some new test strips and I tried one of those, it came out as "low" but I don't want to put too much faith in those, either.

Is it worth taking a sample to a pool store? I have no idea how accurate their testing is for CYA.
 

bradthebold

Active member
Apr 20, 2020
38
Spokane, WA
I just fill the view tube to a line, then glance at waist level. If you see it, add water to the next line, then glance again until you don't quickly and confidently see the dot. The scale is non-linear, so between lines on the tube don't matter. Staring at it and adding a few drops at a time was much harder for me to get something I felt comfortable with as a result. From what I've read, I don't think the pool store will be any better though.