Yep, spirorbid worms is my guess too.
By the way: the polyps aren't healthy. Looks like they are just struggling to survive.
Either the quality of the lights , the intensity, or both.
You probably don't have much water movement there either!
That's what I would worry about..
Be careful when you change. Go slow so you don't damage them.
Specially if you have LEDs!!!
Grandis.