For saltwater tanks you can get a blade attachment for mag scrapers. Actually, one of the large 4" mag cleaners from the LFS may do the job for you, given the inside of it is velcro hook (i.e. scratchy), it certainly removes coralline with some work.
That or you can get 24" long scrapers from the LFS too (well you can up here), so easier to get to without hands in tank etc.