Hi Dong, I've never kept one, but I do remember something that Calfo/Borneman (can't remember which) said at Imac.
Pipe organs are actually a softie, and have flesh down all the way through the skeleton (unlike LPS that just have the surface basically). One of the major issues is that collectors tend to just bust a chunk of rock off and dont go deep enough, so they dont get the matt part of the coral, just the heads, and if thats the case, theres nothing you can do to keep it alive.
Borneman/Calfo said to look at the bottom of the coral, and if it looks like rock, its ok, but if it looks like skeleton, its just going to die on you.