He's harmless and best left in the tank. I have two or three that are that big and tons of smaller ones. Never seen them eat anything that wasn't dead already. One of the benefits of bristle worms not mentioned here is they keep filter feeders fed by spawning frequently. They are good at sifting sand, eating leftover food and cleaning up after the other tank inhabitants, and keep to themselves.
Having a scavenger like that is also nice for when something dies in the tank - often they will pick it clean before it has a chance to rot and foul the tank (had a recent experience with a dead snail where this was the case).
I have a clam, many corals, fish, and shrimp and never experienced a bristle worm problem.