+1 with my friend above. Make sure if you get a frag or anything encrusted with Coralline Algae that it is not exposed to air as it will die off. Release it from the container in its water. It would hurt to scrape some of the C.A. off submerged in the water of the DT allowing it to spread through the water column and attach to rocks, glass and such.
'Purple Up' will not produce Coralline Algae and I intentionally experimented with it with no results whatsoever. I've heard another brand (don't recall the name) but know nothing on that brand.