You said nitrates matched though, right? Might be that the spin test needs an adjustment factor to match the Hanna. When in doubt I alway check a Salifert Alk test. They've been extremely consistent for me so far even between batches of kits tested on the same water sample. Easy titration since the color change is quick and apparent.Dang. I don't blame you. I was just curious because another member commented on my test results from my spin test and in the small sample size ( 2 tests) the spin tests seem to be about 20-25 points off from hanna checker results for alk with the specific spin test brand. I have noticed this on all of my previous tests too.