Here are some posts:
http://reefcentral.com/forums/showthread.php?t=2050181
http://reefcentral.com/forums/showthread.php?t=2057777
My handle is eja99 and you can read about my experience with the CA checker. I called Hanna last week and they said my tester works just fine. My conclusion is that they did not provide the best/correct equipment to run the test given the tiny (0.1 ml) water sample used to calc CA.
I am now going to use a tool that will precisely dose 100 micro liters or 0.1 ml. For the money, it has not been a great experience.