Yep, 20-40 is the coarser stuff . . . I don't recall off hand how they come up with those numbers but even the 30-60 should be fine. The biggest concern are SUPER fine particles because those will make your water murky / cloudy.
As requested: I don't know how this will ultimately homogenize out (in terms of black:tan ratio) But it looks good to my eye. And I had to shoot these with a flash, so the color may be a titch off. In a 72 gallon bow, each 50lbs bag => 1" of substrate thickness (aprox).
^^^ That looks real good! At worst you will end up with a natural "dirt" look if they ever get totally mixed up.
To those other posters concerned about the "shards". I had a few of those I noticed in my 3 bags of the stuff. When I spotted them I pulled a couple out...no ill effects to any of my fish.
Couple of mine were indeed metal shavings of some sort...who knows. After all folks, it's an industrial by-product commonly blasted out of a gun to remove paint off cars, lol. My point being that it probably hasn't been inspected for purity at the level of something that was intended to go in an aquarium. So, as with any DIY project...a bit of self inspection and an acceptance of slight imperfection should probably be the norm. You might wanna sift it, you might wanna rinse it, it might take a bit of work. Good news is you just saved $100 on black sand.
All kidding aside my corys are fine, my shrimp are fine too, and even my "special" oto that thinks it's a cory is fine. (He tries the whole sucky sucky thing on the black diamond substrate. Very funny.)