Disappearing CYA

[mbar]

Owww, my head hurts I will leave this to the chemistry pros, like waterbear and chemgeek. All I know is that whenever I lose chlorine overnight, it is because it is fighting something. If you lose a few ppms it is ok when the water starts at shock. I just think you are asking for trouble when you are playing around with such small numbers as 1ppm to 3ppms to do the work. Just as you said, it is not precise, therefore I would take it to shock and keep it there until the chlorine seems to be holding. You can tell with your own pool, as everyone's pool is different. So you can do as you like, but why are you so adverse about shocking the pool? If you are just after the reasons why shocking is needed, then I will leave it to the chemistry pros

[vinnygnj]

Didn't mean to make your head hurt!

I like knowing the reasons to things.