I agree with flower I think bleaching rocks is an over reaction to something like hair algae.
I have had good luck just doing water changes and maintaining a good cuc in combatting hair algae in the past. some of my previous tanks where overwhelmed with it, my 65g went through a horrible phase. I did very very similar to what star reccomends. I "harvested" as much hair alghae off the rock as possible with a scrub brush in a bucket of tank water, then did very large water changes, in quick succession. the hair algae never came back.