Upgrading to a 125, have a ton of Bristle Worms in my 75. As I move my LR from the old tank, will it do any good to fresh water dip/soak my old rock to get rid of some of the bristle worms, and if so will it hurt the LR.
It would definitely kill off the live rock. To what extent it killed it, would depend on how long you dipped. But that die off would probably lead to a cycle in the new tank. IMO, Bristleworms are great to have. If you have an over abundance of them, it's fairly easy to trap a bunch and remove them. Use a piece of nylon netting, or even a cut piece of nylons. Tie the netting around a chunk of dead shrimp or fish. Tie a string to the trap, drop it in your tank at night and pull it up in the morning. Should have lots of Bristleworms in there eating.