So I read a bit, or hear about zoo's "melting away" from time to time and Im curious if someone could describe this process to me.

Im not really a Zoanthid keeper but with the upcoming grow-out contest I am trying to gather some more info on them.

I got a frag of two lunar eclipse a couple of months ago, one of them is thriving, the other has been closed for 2 weeks and has been very slowly getting smaller. is this melting? or is melting a faster process? I really don't know..