Woops this was supposed to be a response not a new thread.
When I do a FAs-dpd test on my father inlaws pool, after I add the powder abd get the water to turn clear, I go to add the reagent and by the time I pick the bottle up, it is already turning pink again.
I was hoping to find someone else that this has happened to. Except mine turn's back to pink much faster. I get my 10cc of pool water add my powder, water turns pink I add the drops and get to clear counting the drops. Then I set the bottle down and pick up the reagent, by this time the water is already turning pink again, and when I add the reagent, it really goes to pink. I know doubt have CC issues, but I am still not very confident in my result's. This is on my father inlaws pool, 24,000 inground vinyl liner, using tablets. This was the first winter he used the safety cover, and it let a ton of junk in there. When he told me he needed help, it took me 4 days, with constant circulation, and 3 gallons of liquid Cl a day to get the CC under control, begining to look great now!!!
Thanks to all, for all the great info on this site.