I had two bottles of Hanna alkalinity reagent with the same exact batch #. As I was nearing the end of the first bottle, I kept getting low readings... 7.5, 7.6 were the typical values. So I decided to try the new bottle, and I got 8.8 dKH. I tested twice, 8.8 dKH again. I then tested with the old bottle again, 7.5 dKH. I think I'm going to store the bottle in the refrigerator as suggested by @Lasse