im currently using purple up, when i first introduced live rock to my tank it had coroline algae on it already , this was after i had placed a white bleached 13 lb. limestone rock in my tank, i started to get diatoms on my white rock so i got some snails after my cycle to clean up the mess, after my cycle i placed some live rock in w/ the coroline which eventually started to turn black , some coroline bleached out and has still not returned to its normal color, however, i didnt want to loose my coroline and after some research i decided to use purple up, i have a 20 gallon tank and i injected 2ml of the stuff twice a week, and a third time during a water change. w/out scraping the coroline, my white rock started to blush is some places and i have a few maroon colored freckles on my limestone, my original coroline seems to be turning the same color and not as black anymore.
id say that purple up does help.