i didnt bother with my coraline.. some of mine faded white and fell off, some of the other (still red) just chipped away.. some of the white turned green (or i think algae just grew over it) and some of the rock had no effect (maybe it was just paint
)
but, after three months, i can tell that the coralline is starting to emerge on other parts of the tank.. one on the glass, but all over the other rocks.
Just like most things in your tank... i wouldnt bother with it.. it will fix itself over time.