You will notice stuff end up on the bottom of your tank with just rock, I would think i would just be silt and small amounts of detritus produced from whatever is living in the rock.
I went BB and will never go back to a sand bed. I do my weekly water change and siphon the bottom of whatever detritus is there. Unless you are keeping sandbed-living fish such as shrimp gobies or something, there is no reason to keep a sand bed as long as you have live rock. Unless you like the sand bed look better... personally I enjoy the BB look better, plus I don't have to look at 3-4" of sand in the front of my tank.
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Brennan
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