I disagree. 6 inches is barely deep enough to be considered a DSB (5 inches is definitely not) and a DSB is not good to have in the display tank - it should be remote, like in a separate fuge, so it can be disconnected if need be. A sand bed like that has the potential to lead to water quality problems and even tank crashes farther along the road. I would gradually remove scoops of sand until you have 1 to 2 inches. And make sure your rocks are sitting on the glass, not the sand. You don't want a rockslide when the sand shifts. Also if this is in a 20 gallon tank, a 6" sandbed is taking up 1/3 of your tank space. That doesn't leave a lot of room for rock, water or fish.