Help, Magnesium test variations

[Mike.kel]

I have been testing my Mg with a salifert test kit every few weeks getting 1300-1350 as a typical result. However recently I received results from AWT for a test I sent to them and they have my Mg at 1050! My salifert kit does not expire for another 18 months. What could cause such a variation? Should I trust one more than another? Should I add Mg?

 

[Mike.kel]

 

[Randy Holmes-Farley]

I would not assume their value is necessarily correct.