I had something similar on my driftwood, rock work and a few plant leaves. I pruned my plants being careful not to disturb the algae so the spores don't let loose. I boiled the heck out of my driftwood and rocks and scrubbed the algae with a new toothbrush until it was gone.
Here is what Lady Hobbs suggested,
"I have put my wood in a mild bleach/water solution to kill the algae on it. If's already water soaked so doesn't absorb it and I only leave the wood in the solution for a very short time. Maybe 2-3 minutes and then I drop it in a bucket of water with dechlorinatored water and let it soak in there for awhile. It can get in all the little creeves that way and not leave any algae spores to survive.
Several plants can tolerate a mild bleach solution as well. Some don't. (Very mild bleach/water solution.) Like 1 part bleach to 19 water."
If you get it cleaned up reduce the amount of time your light is on and increase your water changes for awhile. Monitor the results and adjust accordingly.
I hate that stuff.
Warning; Bulldog Pleco guarding my Sons tank now..
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