Given my CYA levels, my ideal FC is 4ppm. Although this is ideal for my pool, it isn't ideal for my basic test kit which only goes to 5ppm. Instead of using up all my FAS/DPD test contents from my TF-100, is there a reliable way to manipulate the OTO test? I was thinking something like this: if 3 drops gives me a 5ppm reading, can I multiply that result by the ratio of drops I used to get the proper chlorine reading? IE 3 drops means 40% of the OTO that was supposed to be added, wasn't. So add that 40% to the 5ppm result (5x1.40) for the actual chlorine reading (7ppm).
Is this reliable? Or even correct? I'm no math whiz... lol