You will have worms that even get in on other things you add to your tank, corals ect. My 250 liter reef tank is dry rock and has lots of bristle worms ect. My 900 liter FOWLR has 225 pounds of Caribean Live Rock, KP, and had all kinds of thing I did want at to get rid of. Bobbit worms, Fire works and Red crabs, Even caught a Gorilla crab before dropping the rock in . Mantis shrimp I don't want but cant catch. It killed all my cleaner shrimp... oh well the mantis is cool.
Most worms are good. They clean up and stir up detritus. Bristle worms are the most common. Fires and Bobbits kill fish.... You will probably find more stuff on the rocks.