Went on vacation for 12 days, got home and just tested my alk. Hanna read 8.7 before i left, 11.0 today. Redsea reads 9.2.... i checked the hanna with standard solution, its spot on. I also did a small, maybe 2 gal WC. Fluval 13.5 dosing All For Reef. Should i trust the hanna? Does reagent drift over time?