I wouldn't use silica sand, it contains silicates hence the name silica sand. I used some in one of my old planted tanks a few years back and had algae and cyano like you've never seen. Best off buying new sand or rinsing some old sw sand really well. Atleast you know what's in it. If he's going for planted, i did the back 2/3 with planting substrate, then the front half with 1-2" gravel, then 2" of sand over everything. That way you can plant in the back portion to leave the front open for moss and swimming area. FWIW.
double edit -
this is what I did, which worked really well
p.s. too bad I just tossed 75lbs of white sand last weekend that had been sitting from my old cichlid tank! :P