Definitely not Apex. I know there are people who swear by that. But my experience has been the opposite.
The Calcium and Magnesium numbers will slowly start to drift after calibrating the device. Like Ca showing 200/300 ppm over the actual reading. Neptune's reasoning is that this is happening as the reagent bottle has a needle that doesn't align vertically and incorrect amount of reagent gets pulled. There is a 3d printed reagent bottle cap guides that claims to fix the problem. But I had no luck with that. Neptune support was of little help with asking me to re-calibrate it repeatedly, that never fixed the issue.
From time to time, it would stop with a No Water Sample error. And I would need unplug/re-plug and reset everything all over.