Great. Thanks for that, they can see the logic.
We have the gravel that was in the tank before, which is a mixture of dark stuff (pea gravel) and white.
Some of the white is small white chips. We thought at first it was coral sand as there are a few broken shells, but now we don't think it is, but are concerned it might be Aragonite. It was used before for Oscars, but my lot have a Black Ghost Knife Fish, Gourami, Khuli Loach, etc.
Would it be a problem if it was, and is there anyway to tell?