May not be a spaghetti worm but none of their relatives I have ever read to do harm to corals. I have seen so many "strands" covering a zoa colony that it caused many polyps to close. These worms are regarded as beneficial scavengers but I could see how the mere presence of them sort of smothering a coral could irritate a coral. Manual removal and giving to your LFS may be an option to explore if you have ruled out other potential causes. I didn't see any corals in the video. Maybe a pic or two of the corals showing problems?
Here is an article which contains some info on identifying the worm you may have... http://www.reefkeeping.com/issues/2002-06/rs/index.php
Here is an article which contains some info on identifying the worm you may have... http://www.reefkeeping.com/issues/2002-06/rs/index.php
