Thick is better as far as reducing nitrate. Thin is all for looks and will acumilate stuff with no real benefit beside growing pods. You really need a DSB 4''-6'' to fully work on reducing no3 hth. Did you decide how much sand you are putting in your tank yet?[/Q
I went thin, because I asked the whole world (figure of speech) about it, and did a lot of research, and I learned that a DSB is good for a year or two, but the majority (people who had tanks for 10+ years) of the tanks that had a DSB all crashed, because of the build up of gases, released in their tanks over time, and I am doing this for the long haul.
Yes it is good for nitrates, but there is other ways of reducing nitrates, like vodka dosing, and using Prodibio BioClean, This stuff digests the sludge, and organic waste, and other stuff which reduce nitrates, phosphates, carbohydrates, and other stuff. Of course this means a cleaner, healthier, more flourishing tank, with out crashes!
I know a lot of reefers don't agree with this, so I ask those who don't agree, to go look at LFS's that have been selling corals for over 10+ years, and see if they have a DSB!