Bristle Worms are very good indicator species.
As folks have already posted, there must be an abundance of food if you are having a population explosion of Bristles.
You can try the stocking trick to remove some. Bait a piece of stocking with a pice of shrimp and leave it for a few hours overnight. The worms will get caught in the stocking. Just don't leave it for more then a few hours or you risk fouling your water.