First off, ignore what you were told about bristle worms being bad.
I've had them in my tanks for over seventeen years now and not removed any deliberately although some have been sucked up when doing cleaning chores.
I have many that appear to be well over 8 inches long.
They feed off detritus and any other dying material, and as far as I can tell, get a bad name from some people because they can be seen feeding on corals. In fact, I've also seen them feeding on the corals, but they were only eating dead material that was caused by something else, and possibly were the salvation of some of the corals by removing the affected dead flesh, making recovery easier for the coral.
Usually I hadn't noticed a problem with the coral until the bristle worms called attention to the matter as the part they were feeding on was usually quite small, so then by putting the coral in direct flow of a power head, the coral usually survived the ordeal, even with the bristle worms still eating the dead flesh.