Ton of posts about this...
My experience with algae has mixed results
1. CUC, snails and crabs, don't do much on mature growths
2. GFO does little to nothing
3. ATS turf scrubber, this is the latest thing I've tried, only about a month, I love it so far.
If you want it off your rocks now then reach in and pick it off, there's nothing wrong with that approach either. You need to either prevent what is feeding it or give it a spot to grow, ATS, so it does work for you.