Silica offers no buffering properties like aragonite base sand does.
Aragonite based offers calcium and does a great job pH buffering.
also silica is basically tiny shards of glass, aragonite is round pebbles. for fish like gobies that spend their time sifting sand through their gills its ideal to use aragonite based.
to test if it is silica or aragonite based put some sand in a cup and pour a little vinager over it. if it fizzes(
) you got what you want. if it doesnt you have silica based.