I would say Serpulidae Worm, maybe Spirorbis or Pileolaria
Spirorbis (I have lots of these)http://en.wikipedia.org/wiki/Serpulidae said:Serpulidae is a family of sessile, tube-building annelid worms in the class Polychaeta. The members of this family differ from the sabellid tube worms in that they have a specialized operculum that blocks the entrance of their tubes when they withdraw into the tubes. In addition, serpulids secrete tubes of calcium carbonate. There are about 300 known species in the Serpulidae family, all but one of which live in saline waters. The group is known from the Middle Triassic (Vinn and Mutvei 2009).
Same hereIve got thousands of Spirorbis in my tank with no issues.