I once had bristleworms in my seahorse tank...dosed the tank with Panacur and it killed them off. But it will also kill off fan worms and some other ornamental invertebrates. Might be hard on soft corals too if you have any in there...not sure.
Those bristle worms are making sure of that. If you reduce food waste their population will go down. You can dose the tank with chemicals that will get rid of inverts and kill them off, but I really would just go the natural route and reduce food waste.
why are you are worried about the worms? Every healthy tank has them. Add more diversity of micro fauna and don't over feed. Add some fresh rocks with a higher diversity of life. If the bristle worms are dominate you don't have enough diversity of reef central pest myths. Micro fauna are important. Yes I have bristle worms in my sea horse tanks, thank God.