So I have Hana testers but I got Salifert test kit just to compare and today I tested my alkalinity with Salifert which showed 9.6dkh, Hana 8.2 dkh and then I tried API that was at 8.5 dkh, I did these tests 3 times in a row for all them and always same results. Is Salifert that much off ? which one should I trust ?