I think the question in my original post has got a little lost in all these responses. I truely appreciate everyone's input, but I was not asking a general question about which test kit to trust our which is better or what are the merits of each method.
I was asking: in my specific case, where hanna and red sea matched almost perfectly one day, but then the next day with a new hanna reagent the hanna read significantly lower, what would you do? Furthermore, subsequent hanna reagents have read consistent with each other, which is abut 1 dkh lower than red sea. I'm either at 8 or 9 dkh, neither one is bad, so im not too worried, but it did raise the question.
I guess since hanna is on here, I can ask them directly. ...
@Hanna Instruments,
What would you do in my case? On 7/29 my hanna checker read 8.8. The next day with no significant changes or dosing, the new reagent read 7.6 and on a retest read a consistent at 7.5. Since then, I have raised my alk by dosing 2 part. Hanna read it at 8.1 and red sea at 9.0-9.2. Which number would you take.
At this point, I've settled on not worrying about the exact number and instead looking for trends up or down.