We had a zoa frag that closed up and melted after being in the tank for 5 months. Right after it melted this growth sprung up next to the dead frag. Thinking it was just some kind of algae, we scrubbed it out, but it came back even bigger. It doesn't react to touch (like a feather duster or aiptasia), but we still have no clue what it is. Can anyone help identify it and whether it's an undesirable in the tank? Thank you in advance.

