Your gonna find plenty of bristle worms in your salt water experience. They are there even if you never see them, I promise. If you see them, take them out, especially if they are big. If you can't get them, don't worry too much, they usually only feed on leftover and dead and decaying matter, so they don't really eat anything that you want. If they get too big, they can start to be a pest. Don't ever add them, you already have them! If you see them out in the tank all the time, then that means you have a problem.