It is relatively uncommon for bristle worms to attack living creatures, as others have said.
Possible Causes of Deceased Animals:
1. Temperature spikes during day and you are not noticing.
2. Specific Gravity is off. Be sure to calibrate your hydrometer. If you are usning a floating one, are you doing the calculation to take temperature into account, and if you are using the dip and read ones, have you recently cleaned it (they can become VERY inaccurate within a few months with salt and calcium build-up that's almost un-noticeable).
3. Mantis shrimp or gorilla crab...though neither of these would bother your corals (again, this suggests temp spike or S.G).
Solutions for Bristle Worms:
1. They thrive on too much food. Period. Cut them off for a while. Feed the tank NOTHING. And I mean NOTHING for a while.
2. Once the they are starving (won't take too long...couple days), take a small necked bottle and place a piece of shrimp or other meat in the bottle. Put a 'wad' of fishing line in the bottle all the way up to the neck of the bottle, and place this on the bottom of the tank.
3. Wake up in the morning and you will have TONS of bristle worms in the bottle feasting. The fishing line prevents a quick exit and makes them feel like they are already hiding. Just take out the bottle and dump the worms.
4. Re-load trap and go at it over and over until the bottle stops filling up every night. Chances are your rock AND sand are full of them, and this could take a while.
Fresh water and salt water dips can be helpful for some, useless for others. I've had folks dip the rock until almost everything on the rock was dead (hours, not minutes), and the worms have lived (as have gorilla crabs and mantis shrimps) on occasions. The reasons are simple.....it takes a LONG time for the fresh or hyper-salted water to penetrate "into" the rock. Want a good example....take a kitchen sponse soaked in colored water, and submerge it into a tub of clean water. Very little of the colored water will displace itself from the sponge unless you squeeze it, agitate it, etc. And it's a lot harder to squeeze the water out of the crevaces of a rock. HA! So, if the critters are deep in the rock, they are awfully darn safe for quite some time.
Try the bottle trick for a while, get your camera out, and take some pictures of how infested your tank really is. Oh....by the way....you'll catch the most worms BEFORE the sun comes up! Super-early morning is best.
Best of luck, and God bless.....
