I have actually done the same test with hanna and aquaforest on alkalinity. But i got different results than you. I got at 0.3 differense between them. Both on calibration fluid and saltwater. In calibration fluid my numbers where: Test fluid is 8.2 dkh if i remember correct? Aquaforest measured 8.4 dkh (both of us did), Hanna checker measured 8.1 dkh. I believe you did something wrong with hanna test. You should always wipe of finger prints before inserting into tester, and slowly stir the reagent for 2 min instead of shaking it. I also depends on what hanna model you have. They are both pretty accurate, with a 0.1 and 0.2 from actual target, but when you compare them you get a bigger gap of 0.3