What FH are you using it on? I have black/black tanks but they're not FH tanks. And I would not put my Kamalau or RD in black/black. Already done that as that's how the tanks they are in were set up and they look like crap IMO in that setting. Hell try it I don't care. But your fish will look very dark. And it won't show how nice your fish actually is. Keep your FH ph at 5.0 too while you're at it since we don't care how the fish looks more about how the tank looks.
Black/Black awesome on some fish. But put some FH in it and it looks too dark, don't see the color of the fish/etc. It's obvious black/black makes your fish look dark, white/white makes it look washed out.
If I wanted black sand I'd at least try to use a blue back..