I don't see sand trapping detritus that you can't noticably see. Any courser substrate can.
Have you tried pointing a powerhead toward the rocks to free the trapped detritrus? You'd be surprised how much crap can be stuck in there. I don't particularly like porous rocks.
Have you tried pointing a powerhead toward the rocks to free the trapped detritrus? You'd be surprised how much crap can be stuck in there. I don't particularly like porous rocks.