Black Diamond Blasting sand is from Tractor Supply. You just need to wash it first before you put it into the tank, it's 8.00 for a 50 pound bag. I've replaced it into every tank in the house over the last 3 weeks. I love it and my cories love it. They aren't having issues with it at all, they are pretty much the reason I switched, i love my cories.
As a side note, I have almost used the entire bag it was well worth the 8.00 and the amount of money we saved by using it instead of expensive sand. We used 30/60 grade.