It's not been my experience that dips are effective on bristle worms. You can take a new nylon stocking, add a piece of shrimp or krill and hang it in the aquarium at night when the lights go out, then remove it in the morning, they will get there bristles stuck in the nylon, be careful not to touch it, bristle worm stings are painful.
You can also employ other means, dottybacks love bristle worms and will happily hunt them down and eat them.