Tested my water yesterday and today and am seeing reading of over 500.  Thought at first it could be a bad test kit, but ran the test with both a Red Sea kit and a Salifert kit and got the high readings.
Here are my parameters:
Salinity:  1.026
Alk:  7.4
pH:  8
Mag:  1500
The salt I am using is aquavitro salinity.  
One thing I have been doing is doing a 1 gallon water change every couple of days.  Mixed reef tank with not a lot of big colonies in there.
Any ideas on why it would be so high - I have some white particles floating around so I think it might be parcipitating out but not sure.  You can see the tank here:  
DigitalWeight