New hammer coral isn't opening
 

I got a new hammer coral 4 days ago. It's not opening now, though. It was huge at the store, but now the only part that's showing is a tiny bit on the tips of the heads. Is it normal for it not to open 4 days in?

I drip acclimated it for an hour and turned down my light to acclimate it as well (a little bit at time over the course of a couple hours until it got as low as I was comfortable with—60%—and it still didn't open). My water tested good before I got it, and it's testing all right now. My calcium is looking a little funny; it seems to have gone up in the past day? I've been measuring it and it went from 400 to 350 to 390. I have a Red Sea Ca test kit which is supposed to be more accurate. Maybe it has something to do with magnesium? I haven't been testing that. Would non-optimal magnesium levels make the calcium go back up or did I just do something wrong? I ran the last test twice, so I know its in the 390 range.

Do you think I should just see how it goes? When should I be concerned?

It seems like our hobbyist Ca test kits are +or- 20ppm, so I would bet that is what you are seeing. It wouldn't hurt to bump that up 420 or so.

Do you test for alk? That is a value you need to track.

If you are having trouble raising alk or Ca, Mg can be to blame.

Day 5: Alk is 9, Ca is 400, and the coral is still closed.