Leave it. When you get your clean up crew, they will chow down on it. My army of snails have already turned my rocks completely white, from eating all of the brown algae. Then when the corraline starts to kick in, and completely covers the white rocks, it will look awesome. However, if you feel the need to clean off loose debris and maybe some other things that may be left on the rocks that you don't like the look of.. you can point a powerhead at the spot on your rocks, and then siphon out whatever is floating in the tank. Or use something like a fishing net to snag everything. As for the sand.. when you do your water changes, just siphon out the top layer of the sand. That will get rid of anything that is on top of it that you do not like.