Hanna copper check reliability

[shoelaceike]

Is the Hanna checker reliable? There is always a small amount of powder stuck to to the wall of the reagent packet and there are always particles in the glass vial after shaking. Has anyone checked it against a high end test?

 

[CK00020]

I think it’s pretty accurate if you preform the test as directed, they must allow for a little to stick to the side of the foil