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!