Sounds like you have a porties rock with X-mas tree worms in it. I have never seen them stay out all the time. They always dart into the rock when there is motion. I have even seen them dart in with a wave of the hand outside the tank.
Raise your calcium and your dkh will fall back to a better range they work like a teeter-totter,( with one on each side).
As for the ph if you didn't do some WC's during this vacation period then you may need to add a little buffer, open a window near by and air out the canopy and stand as stale...
I wouldn't put both tangs in that tank. One surely will harrass the other. And I'd wait awhile longer before adding ANY more fish. You just added 5 fish and the tank is new, right? Give the tank and biolgical time to catch up with the new load you have added. My $.02.