you can use "purple up", ive never used it but ive heard that it works. oh, and to let you know coraline algae grows better under low lighting. on my first setup 75 gal. i was running 65x4 watts PC and the entire back of my tank was covered within 3-4 months. now on my current setup 90 gal. im running 250x2 mh and 65x2 pc and only have a few pieces of tank growing coraline, mainly near the top. you can also check around and see if your LFS or a buddy might give you some coraline scrapings off their tank. that will seed your tank for sure! i scraped off all the coraline from my 75 and crushed it up and poured it all over my rocks in my 90 and basically all my rocks are covered!!!