I am testing my FC and TC per the Chlorine Drop Test instructions on my TFTestKit I recently received. Seems rather straight forward but when I add the R-0871 solution one drop at a time the mixture will gradually turn from pink to clear as per directions . But the solution will only stay completely clear for say 30 seconds and gradually I t begins to it go back to a shade of pink--
My question is --Is it accurate to take the reading when solution goes completely clear?? Why does it turn back to pink ? Am I to keep adding drops until it stays clear permanently ?