Try some reef roids or polyp booster to get feeders to come out, then feed it some small mysis. It’s most likely starving, assuming your parameters are normal. High salinity & alk can also make them look like that. My pink one was doing the same thing recently.This red acan I’ve had for about 8 months has recently over the last month started closing up instead of being huge and puffy. It always seems to eat when it’s puffy. Everything else seems fine it’s started as a 4 head plug. All other corals are fine. I use rodi water and do 5 gal changes weekly.