if you're worried about it the rocks that can be taken out can be placed in a bucket of salt water and scrubbed with a tooth brush to remove the algae from the surface of the rocks and then put back in the tank, rocks that cant be removed can be scrubbed in tank. siphon out as much of the floating algae as you can. preferred method is to siphon it through a filter sock so you can reuse your tank water.
what do you have for a clean up crew in your tank?
This is normal, and is all part of the ugly stages that all tanks experience.
You need to arm yourself with a toothbrush and scrub it away each day until it settles down.
Once it is under control add some herbivores like urchins and snails to keep it under control.
You don't mention what size tank, but in a a 20 gallon you should have at least 5 snails and urchin to start with.