If you want the piece left behind to have a better chance of survival, cut it about Â½" up from where it's attached. You can pretty much cut it where you want though. Be sure the new frag
is placed in a similar light/flow area once it's been attached. It will have a better opportunity to recover faster. Once it's doing well, it can be placed in a more desired area that will still meet it's needs.
When attaching the new frag
, a shallow plastic dish with rubble rock on the bottom and veil material/cheese cloth covering the top will be the easiest. Make sure it is in an openly lit area with low water flow.