Doug,
Like Brad suggested the scraping method works great!
When I added a few new pieces of Jakarta rock last year to build my acro shelf I used the same method. I pulled out a small piece of mature rock that was covered in purple coraline. Then I just used a pairing knife to scrape off most of the coraline dust and I let it fall onto the new Jakarta rock. With Ca levels of around 400ppm I had some serious purple rock in about a month or two
