Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Have a look in the lighting forum to see if anyone has checked out the PAR for that light.
The 20 long is quite shallow, so you will get a lot of light.
I like the idea of Eco Complete, but another way to go with black sand is to look into the Pebble Tek product line. This is a quartz material that is added to swimming pools to make them different colors. There are some with real sea shells added, this is not good for a soft water tank, but the pure quartz color blends are good.
Really, though, I would use Eco Complete.
Much better for holding the nutrients for the plants.
You should probably plan on using substrate fertilizers to get started. Neither sand, no EC have any nutrients.