Seachem Calcium versus API Calcium test?

[Enigma]

Anyone have experience with both of these tests?

I've been using the API test for six months. My Calcium has routinely been testing weirdly high (500+). I figured it was due to not rolling my salt bucket well enough.

I just used the Seachem Cacium test for the first time. I didn't believe the number, so I tested again. 300 ppm.

The test is new, not expired, and Seachem just sent me a new reagent 2 (first one was rock hard).

I'm at a bit of a loss. Which test is more trustworthy?