No, it's open. Too high alkalinity can make corals contract.
See if it's receding from the hard skeleton, if so, do target feeding with mouth sized food, 2-3 times a week. Small frozen mysis like Hikari (not large from Piscine Energetics), or LPS pellets that can be cut to the size. Pick up regurgitated food, if there is not enough consumers for it in the tank.