What sniper said. Eventually it will spread. Just leave the skimmer and filters off for a few minutes to let the coralline "shavings" spread around before turning everything back on. I have heard of an accelerator for coralline algae but I have never used it. My lfs
has some but like I said I haven't had a problem with the scraping some off a rock and let it spread method so I never gave it a second look.