Those are likely Spirorbid fanworms.
Vermetid gastropods (or tube-snails) tend to build darker-colored tubes. As already mentioned, the happy tribe of polychaetes include those tubiculous "fan" and "featherduster" worms everyone loves.
Forams? They can tend to populate grubbier, less lighted locations than tank glass, and besides, Spirorbids are a much more common occurence on the glass of new-ish reeftanks.
Your tang is unlikely to eat these little worms, and so too your mandarin, which tends to go after small crustaceans like amphipods. Habitual browse-and-pick feeders like butterflys (or most any other browsing omnivores) will.
Why would you want to kill the worms off?
horge