I have not done any icp tests, idk where to find any in my country. And arent they really expensive?At your current levels it's not urgently bad but high magnesium can hurt inverts over time. You want around 1400 mag and cal 420 to 450. I use coral pro salt also and it works well to maintain numbers. Alk and cal become necessary to dose as you get enough corals which I'm sure you know. Magnesium only depletes at 1/10th the rate of cal and alk so it is fine with weekly water changes maybe a small hand dose weekly.
Have you done a recent ICP test to look at everything?