Black sand? You may want to reconsider and get some fine (oolitic)
Aragonite sand. Oolitic
Aragonite is spherical in shape, so it tends to pack tighter than larger grains, especially non-Aragonite sands that tend to have sharp edges. Packing tighter means more sand per square inch, and thus more bacteria than looser substrates - and it tends to trap
detritus less readily than larger, jagged grains.
The other benefit of
Aragonite is its ability to provide a (slowly dissolving) source of calcium (even at higher
pH levels), thus helping to maintain more optimum alkalinity levels.
