I wish that were true... With so much emphasis being put on rocks and their porosity I would think detritus would be attracted to them like flies to poop. Also, if your not moving your power heads around on a regular basis the flow is probably only coming at the rocks from certain angles. What about the other sides? The currents probably aren't strong enough to do a deep clean either. Also, people tend to forget that Hydrogen Sulfide can form in your rocks too, not just a sand bed. It just doesn't seem logical NOT to blast your rocks with a turkey baster or power head on a regular basis IMO. I'd be willing to bet that those of you who don't blast your rocks probably have all kinds of reactors going, a refugium with chaeto, maybe an ATS etc. If you really want to know how clean your rocks /sand bed are take these offline for a month or so and see what happens.