gbroadbridge
2500 Club Member
A lot of the problems folks experience with the Hanna Ca checker are due to their RODI water used to create the blank has some impurities.
If you have a perfect RODI system it's not a problem, but it only takes the tiniest amount of impurity to result in a incorrect Ca reading.
Easiest solution is to use a certified lab grade RO/DI which you can obtain from many chemistry suppliers including Hanna ( HI70436 for example)
