any time you get LR
from mail order it is highly recomended that you go over it manualy and remove as much die-ff as possible and then cure it seperate from your display tank. anything black or "slimey" is quite likley a candidate for removal. one thing you can use to help you with cleaning is a bucket of fresh RO
water and a turkey baster. Use the baster to blow strong streams of water at the rock. anything that peels off (or starts to) I would suggest removing, unless it is obvious it may be a recoverable hitchhiker you want to keep.