be careful with putting brains in the sand. if you have sand shifting / sifting creatures like gobies, they can build mounds of sand on top of it, and the flesh will die very quickly.
my first thought was that it was a candy cane / trumpet species as well. it even seems to be branching and splitting, which brains dont do. closing up and putting out feeder tentacles is normal operations at night. looks healthy whatever it is, and will continue to look better as it gets accustomed to your tank.