Inconsistent CYA test results

[dojiboy]

As the title of this thread implies, I've been getting inconsistent CYA test results. I have a test kit with the black dot CYA test. Sometimes I get 30ppm, sometimes closer to 60ppm.

I've been maintaining chlorine levels consistent with CYA=60ppm just to be safe (actually a little higher due to above average sunlight, heat and bather load).

So for CYA=60, minimum FC is 5 and target FC is 7.

If CYA=30, minimum FC is 2 and target FC is 4.

Daily FC demand has been 3.5-4.0ppm, and I've found that raising FC to 10ppm at night allows me to remain safely above the minimum FC=5ppm for CYA=60ppm.

The question is, what if my CYA is actually 30ppm? Is FC=10ppm too high to swim in? I vaguely remember someone saying that it's ok to swim as long as FC is under shock levels, which for CYA=30ppm is 12ppm.

BTW, the pool store test result for my CYA is always minimum 100ppm (as high as they will test).

Thanks!

Doji

 

[linen]

Have you looked at the extended directions for the TF100 CYA test? http://www.troublefreepool.com/extended-test-kit-directions-t25081.html#p206397 Might be something in there that helps you. I would disregard the store testing, if you want to check you technique, order the 50 ppm reference solution from tftestkits.net.

 

[Bama Rambler]

Standing with your back to the sun is the best way to do the black dot test. Your result will be more accurate that way.

 

[Vandergraff]

Have you looked at the extended directions for the TF100 CYA test? http://www.troublefreepool.com/extended-test-kit-directions-t25081.html#p206397 Might be something in there that helps you. I would disregard the store testing, if you want to check you technique, order the 50 ppm reference solution from tftestkits.net.

I got the 50 ppm solution for reference.

When I tested it I would have read it as ~70ppm if I didn't know it was 50ppm.

Evidently the black dot has to totally disappear.

As result my pool which I had previously thought was around 40 ppm was probably really below 20 ppm. I have added some CYA using triclor and think I am back above 30 ppm.