Where to read CYA, in sunshine or shade?

[Guest]

My pool used to have CYA 100-120.
I replaced 2/3 of my pool with tap water.
I just test the CYA, but not sure about the results.
If I look at the black dot under the direct sunshine (noon), it's about 40 when the dot disappears.
However, if I look at it in shade or indoor, the black dot disappears at about 50.
So, my CYA is 40 or 50?
This test is really tricky to me, because the "disappear of black dot" is somewhat subjective.
How do you guys determine the "disappear"? The black dot is COMPLETELY gone? or very unclear (something black, but not a whole dot)?
Thank you in advance!

 

[frustratedpoolmom]

outside, direct sunlight if possible, with your back to the sun so your body shields the view tube. It is subjective, I know.

 

[Butterfly]

See if this helps:

Extended Test Kit Instructions for CYA test: extended-test-kit-directions-t25081.html

and make sure you 'see' the visual test, this has helped many of us! ...scroll down for pics..
http://www.taylortechnologies.com/Chemi ... ntentID=44

 

[Guest]

Thank you so much for the links!

 

[frustratedpoolmom]

Thanks Joyce my links are all on my old (dead) computer. LOL too lazy to search for my shortcuts! ;-)

 

[Butterfly]

Both of you are welcome :-D