sandblasting glass beads are an over-kill for substrate use.
they're round for delicate fish
they're fine (like play-sand)
make compacting impossible due to their shape
lots of pore-space for water to keep O2 levels high inside the substrate
the company that manufactures them also produces a ceramic bead for foundry casting, ... but i don't know where they sell it to, ... that i think is white, but opaque, solving translucency issues (if any)
the issues with the glass beads would be translucency, allowing light to pass through, sure glass inhibits UV to a degree, but it doesn't block it, if that's an important factor, an opaque substrate becomes of higher value.
as for ammonia/ammonium & nitrates
bits i've come across don't talk about ammonia, makes me a little confused
they talk about nitrates & ammonium
plants prefer ammonium, failing that their next choice is nitrates that they convert to ammonium
i wish i could find information on ammonia vs ammonium for plant uptake
when it comes to nitrates, the option is to follow what reef tanks are doing with live rock
dead coral rock is great as it allows the bacteria to live safely in O2 deprived water deeper inside the live rock there it can process nitrates into N2, completing the nitrogen cycle, for freshwater if your PH is high (for a chichlid tank sure) can go the same route, ... if your PH is lower then lava-rock would do the job i think (that info is really hard to find