My mag normally drops about 10ppm a week since i've been testing about 5 months ago... i test every other week... haven't been adding any mag recently because I was actually trying to drop it lower.. initially had it at 1430 and i've been wanting to get it down to about 1350.. 2 weeks ago I had it at about 1380... when i tested today, it had dropped down to 1275 based on the salifert test kit. I didn't believe the first time i tested so i tested again and same thing... i have not added any new corals... the only thing that changed was that last week i changed out my older skimmer for a skimz skimmer... the new one is skimming like a beast but could it be possible that it's skimming out my magnesium???