Such a thing as an invisible spider in my tank making a web???

[Kostas]

Ok so I have this piece of live rock, and this hole in it, about the size of an eraser on the back of a pencil.
And it shots out this silk white like web stings, and they attach to near by corals. (and drives me crazy I don’t like the stuff – should I plug the hole?)
Is it good or bad?
Do you guys know what I’m talking about, if not I will post a photo.