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The substrate is "Hawaiian Black" by CaribSea. It's not really black but a blend of reddish and white crushed coral/rock also; but I recall on Maui near Hana that is what the beach is like. Sand doesn't seem to trap waste but it is harder to clean than gravel. The dark background and bottom really makes the fish colors stand out.
The rocks are called "lace rock" and they were bought "dry" (they are not "live rock"), mainly because I think it's difficult to scrape off and control the coralline algae that comes with live rock. The rocks were arranged to create lots of little caves and passages (and there are a lot more in the rock itself). The fish seem to love swimming among the rocks, and the Blue Tang especially reserves a specific cave as its home each time the rocks get moved. The Flame Angel seems compelled to swim through each cave sequentially. The Naso Tang is probably the strongest swimmer, and can get as big as a football as an adult.