Posted this in the general equipment thread and got no real response, so placing it here in hopes of ideas.
So I purchased a second hand KH director, it seems to be working fine except for my KH readings are off from the manual tests I have been using. I changed the lines out, have calibrated the pump head 3 times, just recently changed the KH pH probe and followed the calibration procedure twice and checked with the 4 and 7 pH solution after, and measured the lines properly from the sump. I have primed the lines and made sure there are no air bubbles, and used the KH 7.5 reference solution to ensure the reading should be accurate (my KH director read 7.7 on the 7.5 reference). The problem I'm having is that my KH director is reading almost 1.5dKH difference from the readings of a manual Red Sea alkalinity test (I have used two different lots of the KH titration solution both were within 0.5dKH of each other). My Red Sea test was last at 8.7 and the KH director was reading 10.0. If the 10dKH is right I'm fine with that. Was aiming for 9.0. If it's wrong, then my KH is less than NSW if I let it drop.
So I purchased a second hand KH director, it seems to be working fine except for my KH readings are off from the manual tests I have been using. I changed the lines out, have calibrated the pump head 3 times, just recently changed the KH pH probe and followed the calibration procedure twice and checked with the 4 and 7 pH solution after, and measured the lines properly from the sump. I have primed the lines and made sure there are no air bubbles, and used the KH 7.5 reference solution to ensure the reading should be accurate (my KH director read 7.7 on the 7.5 reference). The problem I'm having is that my KH director is reading almost 1.5dKH difference from the readings of a manual Red Sea alkalinity test (I have used two different lots of the KH titration solution both were within 0.5dKH of each other). My Red Sea test was last at 8.7 and the KH director was reading 10.0. If the 10dKH is right I'm fine with that. Was aiming for 9.0. If it's wrong, then my KH is less than NSW if I let it drop.