Purple up is just a Calcium supplement that really works and I would stick by it. You must have the algae spores in your tank. Ether with rock or scrapings. Most Live rock has it on it, but just waiting for the right conditions to grow well. Good lighting and alk are just some of what is need to grow it. I have found that Purple up works well to accelerate the growth of it very quickly.
Good luck and just try it keeping an eye on your calcium too to make sure its not to high, but if you add it once a week you should be fine. http://www.caribsea.com/itempage_bl...rpleup.htm