My tank has been set up since July. I'm not worried. Just silly things our tanks do to keep us in our toes. I made some of my rocks, used some live rock, and some old rock. Used a couple types of bacteria and live sand and old sand. I know the phosphates are still soaking in and I wasn't worried about the alk drop. I have plenty of corals to soak it up.Any chance you have your tank recently set-up? Sounds like your rocks/sand is buffering, which would be normal in a fairly new set-up. I wouldn’t worry about the dkh drop, unless there is no coral in the tank.
My kh would drop by about 2.3dkh a day if I would stop dosing haha