Planted Tank Guru
Join Date: Dec 2002
Location: Portland Orygun
As for how much take a look at the Sticky post at the top of this forum. Make sure you don't enter total tank depth but the depth of the substrate.
Depending on the sand you can use it as 100% of the substrate. Here in the PNW the sand they sell at the BORG is like flour. And it's a nasty grey color to boot. It would be a disaster in a tank.