How to measure amount of Onyx for tank?

DaveSurfer

Prolific Poster
Mar 14, 2005
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I feel like a real idiot asking this but here goes. I know the calculation needed for measuring the amount of gravel needed for an aquarium. What about Onyx sand? I know it's not as fine as real sand, but the grains are much smaller than normal gravel or flourite...so that would mean that there is much less space between the grains and it would pack much more.

I would have to get more lb of Onyx sand for the same coverage as gravel I presume? What is a good way to calculate this?