Ack ! I wish I had time to babble on here- but I am running out the door. You will not be able to raise your calcium with your DKH at 16 – so that’s not really weird at all. Please read up on Alkalinity by Randy Holmes here: Calcium and Alkalinity by Randy Holmes-Farley - Reefkeeping.com What salt mix are you using? Did you 2x check your test kit ? I’ll be back on the board in a few hours and I’ll check to see if you got the advice you need.