I had that stuff all over my rocks. I tried everything. I finally took each rock out and scrubbed it with a MR Clean scrub brush and clean salt water. It ****ed off all my corals, they just closed up for a while. I then cleaned the sand really well, and did a 50% water change. I used Thrive's phosphate remover, for about 1month. My rock and tank are so much happier now. Have not had a problem with the algae since. And its been about 2 months ago.
In the end, the bottom of the bucket was about 6-8" of nasty stinky algae and what ever else.