1.5dkh lower then my third party tests. It happened after I did my first calibration with fauna Marin. The solution was 6.6 Alk. I did not run a test of that solution right after, but that’s when it started reading my tank 1.5 low. When it continued to read 1.5 low for a week, I decided to calibrate with my tank water. I just left the sample line where it had been, ran the calibration, and it ended about 10 minutes before my regularly scheduled 12a test. It went right back to reading Alk 1.5 low. So no, I didn’t calibrate with fauna Marin or Hanna solution then run a test with the extra solution, but isn’t it basically the same thing when I calibrated with my tank water then ran a test? I gave it confirmed parameters, calibrated, gave it the same sample (my tank water) and it went right back to reading 1.5 lower then what I just told it the sample was. I just got new reagent today. I have a couple days before I have to switch. I don’t understand why it wouldn’t hold my tank values, but when I calibrated with tridents solution after my phone call on monday (which I tested and Hanna/Salifert both read. 85 higher) the trident now reads .85 lower each time. When I spoke with Carlos, he mentioned that “trident is smart enough to know if the value you give it is too high, and if it detects this during calibration, it goes back to its last successful calibration.” His example was if I accidentally entered 80.5 for Alk instead of 8.05. I think he was trying to convince me that when I calibrated with my own water I entered an erroneous Alk number. But the calibration wizard won’t even let you put in a number that is out of range. I don’t know. If it won’t work after I switch reagents, I’m going to ask for an exchange now that I see SEVERAL other people who just purchased it are having the same problem.