2 or 3 inch bed in the DT may cause problems in the long term. Sand beds should be 1 inch or less or 4 inches or greater. Depths in-between cause problems. Take the extra sand from the display and make your DSB deeper. This will cause a higher rate of dissolution and nitrate reduction as well as provide plankton to the rest of the system.

I am a proponent of sugar fine oolitic aragonite for all sand beds. It produces the anaerobic layer at a shallower depth.