If anyone has a Hanna Alk checker, go to the MTRC site and look for the thread on Hanna Alk reagent issues. They have found that some batches of their reagents are bad and give low readings. I had been using the Hanna checker exclusively and just happened to get a salifert Alk kit from josh. I compared the results and they were quite a bit different. The salifert kit included a Alk standard and I ran a test to compare the 2 kits. The standard was 2.40 meq/l. The salifert measure 2.39meq/l. The Hanna measured 1.50meq/l - quite a difference. Hanna is offering to replace the defective reagent. There is a lot of good information in the thread.