If these guys have convinced you to consider white sand I would add that Nature's Ocean live sand is what I used in my 29g mixed reef. This company's products can be found in many lfs. I have a deep bed of their Natural White #1, which is quite fine, and on top I have their aragonite live reef substrate, which is a mix of small shells and coarse sand. The latter helps keep that fine stuff from going all over the tank. My invertebrates and a few of the fish I have had love digging and if those type of animals interest you then you should consider this type of combination because it allows them to have at it.