wait, stop supplementing. do a water change if it's high enough to be in the danger zone... check your Ca and Mg, get those to NSW levels. IMO don't worry if it's not over 14 (edit: 14 dKh).
Here is table below shows a series of balanced combinations of calcium and alkalinity in modified seawater. You need to balance Calcium and Kalk base on this table (dosing Calcium or Kalk to get balance)