high Alkinety and low Cal

[keeponreef'n]

ya i don't know what happened just the last month everything all of a sudden changed! been using Aqua Forest reef salt weekly water changes of 10%. LFS also says give it time! My aquarium is 9 months now so i added some coral which all died the past month! but ya Mag is higher then 1600 , Alkinity is top of chart also and my Calcium is low ! Is there any suggestions on what brand i should start to dose Mag with ? thank you for your input also !