high alk and low calc

My tank chemistry got messed up in a matter of 2 days out of no where Mag: 1130 Alk: 12 No3: 1 Po4: 0.07 Ph: 8.3 Ca: 200 I will do a 40% water change tomorrow Please give me some tips on what to do to fix this high alk while increasing calc I was dosing all for reef I had one of my wall...