At this point I would probably do a Triton test just to see if something pops up. I skimmed back through the thread and I see you used two methods to check your alk, so its probably pretty close to what you think it is (which was 8.4 or so on the tank, and 6 or so on the fresh mix). That seems like a really safe number to me, it's what I strive for. I am hoping with time, monitoring, and water changes it will resolve itself, but it may never be explainable. I can give you more tester frags whenever you need them. And when you feel things are stable we can work on replacing various ones you got from me.