Bubble corals can be a little picky about the flow they're in. Too much or too little and they won't fully expand. Have you tried moving it to a different area? And it needs to be in full light.
Okie I will try and move him then ....what type Of flow and light do they like I was under the impression they like minimal flow and not so high of light ? Mines in my sand bed
Oh man sorry to hear that ( but ill try and feed it some brine shrimp now and see what happens next couple days...how often did you feed yours?
I would remove it from the sand. Put it up in the rocks. Here is a picture of mine. It`s 15 years old this month. BTW never have target fed it. It gets all it needs from the lighting and water column.