Many years ago I got some black blasting sand made from slag. I never used it as I felt it was too sharp. I ended up throwing it out. maybe I got too fine a sand.
The thing about sand or gravel is haw smooth or edged it is. For pool use they want the edges. As the sand tumbles in the filter it gets smoother until it stops working well and must be replaced.
In the 70s I worked construction in Saudi Arabia. My first year I ran a large concrete batching operation- we produced about 200,000 cubic meters. I had to learn a lot about concrete fats. Basically concrete gets it's strength by mixing small particles (sand) with larger particles, aggregate, and then glues it all together using cement and water. The sand fills the smaller spaces and helps hold the stones together. When it all dries is it very solid.
In a tank something similar can happen except the is no cement. However, mixing a variety of particle sizes can compact. But using a lot of fine sand can do the same. The smoother the particle and the smaller the size, the less change there is for space between them. In concrete the space is filled with the cement sticking it all together. In a sand substrate compaction happens the smaller and smoother the sand grains.
If you co to CaribSea's site you can see the data on the Super natural Substrate. The give the sizes for the sand and gravel. Here are the sizes for the sand particles:
Moonlight-
Typical Size: 0.25 – 0.75mm -
Average Density: 95 pounds per cubic foot
Sunset Gold-
Typical Size: 0.25 – 1.0mm -
Average Density: 94 pounds per cubic foot
Crystal River-
Typical Size: 0.5 – 1.0mm -
Average Density: 95 pounds per cubic foot
Torpedo Beach-
Typical Size: 0.5 – 2.0mm -
Average Density: 94 pounds per cubic foot
The finer the sand the heavier any given volume. Pictures of them all here
https://caribsea.com/freshwater-substrates/
One thing about black sand is it shows off any dirt, debris and poop on it like a neon sign.
I used the Estes Bits of Walnut, a pretty small sized gravel, in my high tech planted tank. All plants did well it it. I made the mistahe of using large sized rounded river gravel in my clown loach tank. It is almost impossible to have plants in the substrate with this. I managed to keep big swords plants though. Most of the plants were on wood or rocks. (below is a pic- it is a 75 gal tank)
