Well, I had errands today that would take me by two pool stores I have used in the past. One of them really likes me because I purchased my Dolphin M5 and a stand alone hot tub from them.
So here is the test, three samples of water, all taken at the same time. I tested one at home and took a sample to each store. The only difference was drive time for the tests.
Store #1 Results (BioGuard automated testing)
Recomendation - Acid to reduce pH
Store #2 Results (hand tested with Taylor chemicals)
So, maybe it took me an hour to get to store #2. Is a FC drop of 5.0 in an hour possible?
I still trust my numbers more than theirs.