need help!

[makana]

I have a 29g cube. My bubble coral has been looking sick the last couple of days. One side doesn't inflate at all and the other is half inflated. I added an open brain coral a week ago. I've been looking for pests on the bubble coral but there is nothing I can see. Amonia 0, nitrite 0, nitrate 0, phosphate 0, ph 8.1, alk 1.8 meq/l or 5.04 dkh, calcium 380.

I've never had calcium and alk go low like that before so I'm not really sure what I should be doing to raise them back up.

All I have is the bubble, brain, and a sun coral so I don't know why I have this dip. I'm going to do a water change tonight to see if that helps.

Any suggestions?