Inconsistency with FAS-DPD test

[A_kraker99]

Has anyone every tested the same sample of water multiple times and gotten very sporadic results?
I just did the test on the same sample of water 30 minutes apart and my first test was 20 drops and the second was 25. I am a pretty good about rinsing the tube, precise fill levels and wiping the dropper tip before starting drops. I also use the auto stir. My understanding is that the amount of powder used is not really that critical. I usually just do 1 heaping scoop.
inhave had this inconsistency a couple times now. It usually results with the later test reading a higher FC level. Is there something happening with the water sample when it sits in the sample bottle for 30 minutes?

 

[GuinnessPhish]

no need to wipe the dropper tip during the chlorine test.

 

[A_kraker99]

no need to wipe the dropper tip during the chlorine test.

I thought there was static buildup that could affect the drop size?

 

[GuinnessPhish]

I thought there was static buildup that could affect the drop size?

pretty sure that's only on one of the other tests.

 

[Sunnydaze]

Occasionally, I'll do the FC test and get results lower than what I expected based on knowing how much FC my pool consumes each day. 1 to 2ppm low. I'll retest and get a higher result which is in line with my every day testing. I chalk it up to not using quite enough powder when that happens. It doesn't happen often but it does happen and I just get that hunch that it's wrong because my fc loss is very predictable.

Edited to add: when I've retested, it's a fresh sample from the pool and less than 5 minutes apart.

 

[mknauss]

pretty sure that's only on one of the other tests.

TA