Have you used it before? IMO the weak link is the darn micropipette. Unless you work in a research lab I think it's easy to miss-judge the "stops" when using it. There is a bit of feel that goes into it, and when your total added test sample is 0.01ml, well, it can be inaccurate. The other source of error (and, hey, maybe this is it) is that it's hard to be sure you got all the powder from the packet...if any is left behind, or you spill the slightest amount, you're gonna be off. I have finally started getting accurate readings on mine, as I always run it against a simultaneous Red Sea titration for Ca. I started way off, like you, but now they're matching up, so, again, I assume it's user error. But don't feel bad. BTW, I think after this experience that the Hanna isn't worth the trouble. It's actually silly how much user error is built in. It's not easy like their alkalinity (that's sweet, simple, fast, and accurate...well worth the $), so I'm sticking with the titration tests.
