+1
First, be patient. Do your water changes and do as much manual removal as you can with each water change (I use a toothbrush, it's really not as tedious as it sounds, maybe 10-20 minutes) but don't go crazy and try to get rid of it all at once (I would only do 10% weekly or 20% biweekly). I'm guessing your system is new and it's part of the typical cycle that can happen. Don't go crazy with getting a bunch of "cleanup crew", in the long run you only need a few herbivores. My prefferences are blue knee hermits, Sally Lightfoot crabs (only 1 or a male/female pair if bigger than 50 gal) and my favorite, Tuxedo urchins (short term maybe several but long term 1 per 50 - 100 gal). Corals are competing with algae for the various forms of organic and inorganic nitrogen and phosphates so I would be adding easy corals as soon as possible (there's lots of polyps, soft and stony corals that will work). Did I say be patient?