The other day I became suspicious that I wasn't using enough DPD powder for my OCLT testing. I tested my water 3 times the other night and got different results each time (frustrating). I decided last night to use 2 heaping scoops of the DPD powder (goal FC was 20) and came up with result of FC 22. I decided only to test once so as not to drive myself crazy. This morning I tested with one heaping scoop (forgot the 2) and came up with 20.5, then did the test again with a slightly more heaping single scoop and came up with 21.5, then gave in and did 2 scoops and came up with 22.5. I've been doing the OCLT for 3 nights now and am pretty much at the point of just stopping because I'm a little frustrated with these results. I think we're fine - we've been .5 away from passing the past couple of nights, and I think it might just be testing errors.
How many scoops should I "really" be using when I'm shocking at 20?