Water changes to help them fall in line. Of the three your alkalinity is more important. Get that in line first, then work with the other two.
What are the PH and salinity, salt mix?
Since talking with Kipass about a week ago I have found more information about execss of Magnesium in aquariums. It seems that excessively high Magnesium can relax or anaesthetize and can harm in marine organisms. In one article that I was reading they were talking about 5 or 6 times NSW mag levels causing problems within 30 min. As you may know 1300 ppm is normal, 2000 would be cause for investigation. What are you adding that makes it so high?
It also seems that Magnesium Chloride is a better choice. I have read where Mag Chloride at a certain excessive dose makes a good relaxant the same dose of Mag Sulfate (which is what I use, Epsom salt) can cause death, not a good thing, but so far after a couple of years no problems on that with me.
Your best bet is to do some water changes to try to get your Cal,Alk, and mag in line, buffer to help get that alk up until your cal gets to about 420 then maintain that as well, your water changes should fix your mag unless your salt has a low content.
Thomas