Emm,
My rock bog is at the top of the stream. It is about 7' long, 3' wide and 2.5' deep. The 2 (4,500gal/hr each) pump hose outlets are buried in it. It overflows to creat the streams. I have plants in the rock around the perimeter and barley straw floating. We add Clarity Max weekly. The water is really clear, it's magic. We have no other filtration other than the skimmer. People talk about sludge in the bottom of their ponds, but so far I don't have anything but rock. Maybe a different story when the fish grow, though.