Using a TF-100 my CYA reads zero. (I can see the black dot when filled completely.)
But I know it is not zero. I had the local pool company test it twice 2 weeks apart and they have a reading of 30 ppm both times.
Also my SLAM calculations are jiving at 12 ppm shock level when I add/test; so I am inclined to think pool store is correct.
I am certain I am following the instructions correctly.
Could the R-0013 Reagent go bad?
Does anyone have experience with inaccurate CYA testing using the TF-100?