Dropping from 33 to 30 overnight? Perfectly normal! when you are super-shocking it's harder to maintain the FC...and you only dropped 9%. I wouldn't worry about that at all.
What I'm wondering is why your CC is so high and not dropping with FC > 30.

PS: I'd run the FAS-DPD test using the 5ml line instead of the ten. If you don't have that line you can either guess where it is or use a kid's med cup that comes with cough medicine with a 5 ml line. Each drop then is 1 full ppm rather than .5. It will take less time to do the test, use half the R-0871, and certainly be accurate enough at those high FC levels.