Coralline algae is a calcerous algae that is considered beneficial/non detrimental in aquariums. It comes in many colors (determined by species of algae) from pink to purple to green to red to brown to black. (If you'll look through the photo album at some of the SW
photos, you'll see many peoples aquarium glass and rocks covered with pink, green and purple coralline algae) For cultivation...maintain NSW
(natural seawater) levels of Calcium, Alkalinity and Magnesium and you will find coralline growing all over the place within a few months. It is a good idea to seed your tank with some coralline (either scrapings from someone elses glass, or a piece of LR
with good coralline growth on it, pointing a powerhead at the coralline on the rock will encourage it to spread to other areas of the tank, by distributing the spores.