Sandlike substrate, but easily vacuumed.

[freeblackfish]

Does anyone know what substrate was used here? The designer, Jeffrey Senske, never identified it in the two-part article he wrote about the design. He merely says:

After assessing several contenders, I settled on a product I had used often in the past for its sand-like texture and grain that also happened to be large enough to vacuum. Coupled with its bright, clean look and consistent coloration, the substrate issue seemed solved.

I guess he wanted to keep it a trade secret, but does anyone know what he might have used?

Thanks!

 

[Peach02]

Pretty sure that’s sand or crushed coral skeletons which is more or less sand. Both are easy to vacuum