raising magnesium

Hey Doc! I was talking with a buddy of mine and he was telling me how he just purchased a Red Sea Magnesium test kit to test his magnesium for the first time. He said his mag came in around 300!?? I didn't see his tests but he swears his calcium was close at 400 and his Alk was sitting right...

So I have been testing my water Everyday and my parameters are 420 Calcium 8.5 to 9.3 Kh 1200 Magnesium Started adding Kent’s magnesium for 3 days and can not get it to Raise. Any Advice ? Would be much appreciated have a Kung Pow Monti on the way and would like it to be around 1300. Also...