Personally I like to use aragonite based sands in a marine tank.
Aragonite contains calcium carbonate and some strontium and magnesium.
These compounds and elements will dissolve back into the water over time.
To what degree, is highly debatable, and it's dissolve rate is determined not only by tankwater's pH, but to some degree by the wastes produced by the living creatures, worms and bugs down in the sandbed.
Black sand is not made from aragonite, and will not contribute much to your tankwater chemistry regarding calcium, carbonate, other trace elements.
I don't know if it will harm anything using this black volcanic sand.
Some folks feel that it will certainly provide areas for nitrifying bacteria to populate and colonize, which provides excellent biofiltration and may aid in denitrification as well if it's the right depth ( and is alive with the sandbed critters ).
Sand choice is like many choices in this hobby.
All depends on who you talk to or read, and what you feel is best for your own tank.
I like aragonite - it contains stuff that is in seawater.
Other sands do not.
Most everything dissolves over time in saltwater. If and when it does, I like it to be beneficial.
This is just how I feel about sand choice.
