Blasting grit is usually sharp edged so it cuts better in its intended use. I used to use a black blasting grit that was made from coal slag. It killed all of the Cories I tried to keep by damaging their mouths. So, I swore not to try that again. Now I use a lighter dark grey Soilmaster material and Cories have no problems with it. I really did like the appearance of the jet black material though.