Which Ca test to believe?

[hllb]

I bought a used Hanna checker off eBay. Seems to be in excellent condition and the reagent expires in 2021. Tested the water tonight and got 492. Tested with my Red Sea test kit and got 335. That’s a huge difference! How can I tell which is closest to correct? The water is a mix of IO salt and Reef crystals (last few 10% wc has been w reef crystals, 32 g tank).

I still need to test alkilinity but it has always tested around 9.1 with Red Sea and the ca is usually around 360. I have live rock, a Duncan, a monti frag, and an open brain in the tank.

 

[Willu]

the calcium hanna checker is known for its low precision due to the precise requirements of the test(i.e the dilution step), and so I would probably go with red sea given that you are doing ti correctly.

 

[hllb]

That's a bummer - I wasn't aware of that but I see it's discussed frequently. Looking back at my Ca tests, seems I'm using about 5 a day, which kind of surprises me. I guess I need to start reading up on dosing. My alk and mg are fine, so it's just calcium that's an issue.