Black Diamond Blasting Sand is great. Especially for planted tanks. About $10 for a 50 lb bag from Tractor Supply Co. Much more expensive anywhere else. But a lot of people don't understand just how much prep work it is or just how important it is.
First of all, go with the 20/40 grit (medium). The finer one is just too fine and dense..not great for plant roots/diggers. Just like others said, it's coal slag by-product. Machines that are used often are also working with metals so get a high powered magnet from home depot.
Having a large tank means HOURS of cleaning. Soaking in hot water. Stirring and agitating. Dumping the dirty water. Over and over. Doing in smaller amounts (think like 4" of sand in a 5 gal bucket) with as many buckets you have actually makes it easier. DON'T DO THIS IN YOUR BATHTUB. VERY BAD FOR PLUMBLING LONG TERM. DUMP THE WATER OUTSIDE. Once the water is clean from hot water, you can take it outside, stick a hose in there, and let it overflow for a bit. It's heavy enough to not overflow with the water. Go overboard. Clean it more than you think you should. You don't wanna deal with the oily film in your tank.
Run that magnet through it over and over. Better safe than sorry, and you'll see what I mean. Oh and an old pillowcase works magic. Sand in pillowcase..acts as a durable strainer.
Do you really have to do all this? I guess not, but the people saying it wasn't good for their diggers/corys/bottom dwellers with barbels..probably didn't do all this.