Problems with GHL KH director

[Jubei2006]

So I purchased a second hand KH director, it seems to be working fine except for my KH readings. I changed the lines out, have calibrated the pump head 3 times, just recently changed the KH pH probe, and measured the lines properly. 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 my readings on my manual Red Sea alkalinity test (I have used two different lots of the KH titration solution). My Red Sea test was last at 8.7 and the KH director was reading 10.0. Will check again today. But not sure which one to trust. Thanks in advance reefing family.

 

[CNDReef]

Is the kh reference solution been open a long time? Or contaminated in any way?

 

[Jubei2006]

Reference solution is brand new purchased 2 months ago and just opened for this problem. Ran 3 times with said solution got 7.7 twice and 7.8 once. Did a full flush with the reference solution twice to make sure no tank water contamination was present prior to running the solution. The old probe was also running KHs within 0.5 dKH of the new probe. So may be getting a Salifert kit to also check.

 

[ReefLK]

I have a KHdirector and for a month I have lost the measurement and now I receive measurements with 0, after that, I cleaned the heads, I calibrated probe and pump, a provider told me that the PH probe was damaged, but I tried the probe in another unit after all, and there it works perfectly, and my unit keeps showing 0, I don't know what it could be, could you help me?