Small bristle worms are not bad for a tank because they are detrivores. They'll help to eat up any uneaten foods lying around. It's only when they are overfed & become "monsters" do they usually become a problem. Mine will bite corals (bit my red brain last week
), so I'll have to deal with it soon via a free tour of the Burnaby sewer system. Watch how much and how often you feed & your bristle worm population should never explode & become a problem.
By the way, always try to catch them with a net or container & not with your hands or you'll be scratching for a week from the bristles they leave behind. (Do as I say, not as I do
)
Anthony