Not exactly what you asked, but I got a tank for free with this stuff in it and I immediately threw it out to replace with regular gravel. The hard little balls are perfectly sized and shaped to trap all sorts of particulates, and unlike aquasoil this stuff doesn’t break down into dirt/mulm. I can’t think of a single reason why this would be superior to any other kind of substrate, advise you choose something else if you still can.
Regarding capping substrates, you really only need to do so if you’re using potting soil (thick sand cap keeps it from flying everywhere clouding up water). Most of the time leaving substrate uncapped makes for a neater look, plus gives you more reuse value because it won’t be all mixed up
In my experience, using this and sand together, without some serious effort to prevent mixing, they’ll mix. When they mix it becomes very dense and kind of defeats the purpose of having it. I’d go with one or the other personally.
veez981 
Not exactly what you asked, but I got a tank for free with this stuff in it and I immediately threw it out to replace with regular gravel. The hard little balls are perfectly sized and shaped to trap all sorts of particulates, and unlike aquasoil this stuff doesn’t break down into dirt/mulm. I can’t think of a single reason why this would be superior to any other kind of substrate, advise you choose something else if you still can.
Regarding capping substrates, you really only need to do so if you’re using potting soil (thick sand cap keeps it from flying everywhere clouding up water). Most of the time leaving substrate uncapped makes for a neater look, plus gives you more reuse value because it won’t be all mixed up
I mixed mine with regular gravel because I wanted the benefits without the ugly look. I’m pleased with how it turned out.
My tank is low-tech, so this wouldn’t work if you’re going for fancy.
It’s a pain in the ass to plant into. I don’t think it has any nutrients.
In my experience, using this and sand together, without some serious effort to prevent mixing, they’ll mix. When they mix it becomes very dense and kind of defeats the purpose of having it. I’d go with one or the other personally.