We just had a discussion on types of black sand used, over on the setup subforum. I use Black Diamond, purchased at Tractor Supply. I get the 20/40 grade. One of the complaints made against it by a poster is that it did or potentially shreds the barbs of their cory cats. My daughters have cory cats in both their tanks, and I have black diamond in theirs and their barbs are quite long and the fish are constantly getting in to something.
There are a bunch of types to use:
Black Diamond
Black Beauty
Estes bought out 3m colorquartz and thats what I used to use, and people like that as well.
For a price reference Black Diamond is 8$ for a 50 lb bag.
No matter which you get, it'll need to be rinsed out thoroughly. Every single one leaves behind a very staining residue. If you notice an oily film in the water when you first put it in, you didnt rinse it well enough. Just run a few pads of polyfilter for a week, changing each day and it'll clear out just fine, with no harm to the fish.