Hanna Calcium Checkers

[Myka]

I have been using clients' Hanna Calcium Checkers on their tanks (I do aquarium maintenance) and I've been assuming it's correct, although I've had a few abnormally high readings. I use Elos on my own tank at home. I recently bought a Hanna Calcium Checker for my own use. I am always in the habit of cross checking new test kits with old test kits.

So I tested my water:

Elos 365 ppm
Salifert 360 ppm at LFS
Hanna 435 ppm (tested a few times)

I've heard lots of people saying that the Calcium Checker reads high. It seems it is certainly higher than Elos and Salifert.

To add to the confusion, this is on a tank that I'm not dosing at all. I'm using H2Ocean salt. I got the following results for alkalinity:

Elos 8 dKH
Salifert 9 dKH at LFS
Hanna 8.5 dKH (153 ppm)

I know that it is "normal" for Salifert to read 1 dKH higher than Elos. Hanna is right in the middle. All three of these numbers are perfectly fine by me, so I'm not too concerned here.

Now, the confusion comes here...since the tank is not being dosed (just bi-weekly waterchanges), and I'm using H2Ocean salt, you would expect alkalinity to get low before calcium, but the alkalinity in the tank is barely lower than the alkalinity of the freshly mixed saltwater. One would then expect that the calcium should be close to the freshly mixed saltwater too. So, is the Hanna Calcium Checker actually accurate in the 435 ppm range??

Are you all getting accurate results with the Calcium Checker? How is it matching up to freshly mixed saltwater and other test kits? I'm using my own RO/DI water at 0 ppm TDS for the calcium checking, what are you all using? Using such a TINY amount of sample water has me wondering on the ability to accurately measure. I have been trying REALLY hard though.

Please share you experiences!

Edit: I just thought of something...I'm going to go measure the freshly mixed saltwater with the Hanna Checker.