Remove the rock, put in tub or pan & try to pry it off (without popping it), then rinse well in new ro/di & put back in tank off to the side away from other rocks until your sure it is gone.
Whatever you do, don't pop it. I'd also look around for others because usually if there's one, there is more...Atleast that's what I was told and they were right
ACK! More? ok I am getting out my strong reading glasses ! There is a sponge (pink) that I like on that rock so I think I am going to try the chipping method.
personally i don't bother trying to remove it anymore, half the time anyways people look at my tank and it's the first or second thing they notice, and they think it's cool...lol
i have used a turkey baster to get the little bubble algeas you just have to put the bubble in the intake and slide baster against rock and allow to suck up once loose. the has been the easiest way i have found to do it and you dont have to move the rock at all,