i've used large river pebble, small river pebble, black aquarium sand, and play ground sand which i currently use on my 240g african cichlid tank with about 30-35 medium to large fish and i will never go back to rock/pebbles...i rinse half a bag at a time and do so about 5 times each half, water clouds about 5-10 minutes then clears very nicely, its alot easier to keep clean and looking good, i simply vaccuum the poo off the top once or twice a week i can vaccuum a top layer of sand out and it doesnt matter cause i can always add more since its so cheap.