Cool. Where did you find that? The equivalent is Black Diamond Blasting Sand found at Tractor Supply. Lots of people have used that as a substrate. As it says, it’s the slag from iron smelting. Some reports say that if you drag a magnet through it, the magnet will pick up iron particles. I’m pretty sure that Petco’s black Imagitarium Aquatic Substrate is the same thing, just more refined.
I use the Imagitarium, but only because I didn’t know about these cheaper substitutes. All are inert, so you will want to supplement. I suggest that you get enough to get a total depth of about 2.5 inches across the aquarium. Put in 1.5 inches, and then mix in some unadulterated potting soil (no added fertilizers) so there’s a 10% to 90% soil-to-grit mix. Put some root tabs on top, then add plain grit (one inch) on top.
Potential_Status3460 
Cool. Where did you find that? The equivalent is Black Diamond Blasting Sand found at Tractor Supply. Lots of people have used that as a substrate. As it says, it’s the slag from iron smelting. Some reports say that if you drag a magnet through it, the magnet will pick up iron particles. I’m pretty sure that Petco’s black Imagitarium Aquatic Substrate is the same thing, just more refined.
I use the Imagitarium, but only because I didn’t know about these cheaper substitutes. All are inert, so you will want to supplement. I suggest that you get enough to get a total depth of about 2.5 inches across the aquarium. Put in 1.5 inches, and then mix in some unadulterated potting soil (no added fertilizers) so there’s a 10% to 90% soil-to-grit mix. Put some root tabs on top, then add plain grit (one inch) on top.
Look up cation exchange capacity (CEC) to see why the potting soil is important: https://en.wikipedia.org/wiki/Cation-exchange_capacity
I used the black diamond version to cap mineralized top soil. Works great. This is how I got the dirt ready:
https://www.aquaticplantcentral.com/threads/how-to-mineralized-soil-substrate-by-aaron-talbot.52554/
It is fine and I’ve been trying to find a bag of coal slag with no luck. No Tractor Supply in Canada.