I've had to resort to filling two vials, one to use with the reagent and one with just the tank water to zero the unit. And, of course, getting all of the powder from the packet to the vial is difficult. As a result, I'm never quite confident in my results.
It's not as big a deal as it seems.....as was mentioned already, Hanna even says the residue left in the packet is OK. Do a good job, but remember that consistency between tests – being able to compare your own results – is always the real key for these things. Don't worry about being perfect, just be good and repeatable.
As for the checker, sometimes it stays on longer then 2 minutes and sometimes it shuts off exactly at 2 minutes work. I can't figure that out.
If you hold the C2 button down for several seconds it sets off a timer instead of taking an instant reading.
I'm not that concerned about perfect accuracy, so I also "dual-vial" my phosphate tests on the checker....but I am also careful about de-fingerprinting the vials. I also take several instant-read comparisons after the main to see if there's any inconsistency. I'd re-test from scratch if there was any major inconsistency.....otherwise I usually go with the first result.
Wish my vials didn't leak....other than that I like it a lot.
@RyanCSGO Calcium is a difficult test to run if you're already used to running drip tests. If you're familiar with lab gear and procedures, then it won't be as big a deal. Personally, it took me quite a bit of practice to get my test results to match 1:1 with my Salifert kit.....but I did get it. They other kits are significantly easier to use. I wish they made one for Nitrates.