Discrepancy between Red Sea and Hanna calcium test

[ScubaSkeets]

Hi folks!
I just did a calcium test with both Red Sea and Hanna. The Red Sea showed 425ppm and the Hanna showed 550. I did the tests twice just to make sure I didn't do something wrong and none of the reagents are expired. Any ideas?

 

[schuby]

Yes. You must use distilled water for the Hanna checker and not RO/DI. The RO/DI water likely has some calcium in it causing the checker to read high. I had this same issue at first. Rinse with distilled water, too, before starting to test.

 

[ScubaSkeets]

Yes. You must use distilled water for the Hanna checker and not RO/DI. The RO/DI water likely has some calcium in it causing the checker to read high. I had this same issue at first. Rinse with distilled water, too, before starting to test.

Thanks. Yes, I did think it was the RODI, but the video did say use deionized or distilled water, so thought maybe that wasn't it. I'll go get some distilled water.
Thanks again