Briareum species?

[dizzy]

I got this small species of plain looking brown briareum (I think) on a piece of live rock or coral. It started out in one place in the tank and grew to cover almost every exposed square inch of live rock in the 160-gallon tank. At first I thought it was attractive and wasn't too concerned, as it didn't seem to have a deadly sting to the other corals. After awhile a lot of it started to die. I was able to peel some of it off the rocks and it had grow on a sort of soft algae type mat. In places it is gone and a small white root looking is left in the wake. The polyps are about 2mm in diameter tip to tip. The white root can be seen in the second photo with the red serpent star. Does anyone what this stuff is?