I just now started noticing them in sump haven't seen them in display yet and i hope i won't however i have fish gone missing with no health issueI do think that having no bristle worms in the tank is near impossible. When you have live rock in your tank that is. On frags they probably be killed of when you dip the coral? But it only takes one or 2 to slip trough the net over time and they will grow their numbers. Do you have none in your tank or when you see one it's priority number one to get it out?