> Whats substrate? I usually use just gravel, or is substrate for salt water
 > setups?

Gravel in generic is substrate but it comes in several forms and some are
sands while others are big rocks.  I have simple colored gravel (green and
blue with a smaller bag of 5lbs or so white at the back for contrast).

Charlotte added several glass marbles.  Don added a sunken ship with a hole
smaller ones can hide in or swim through, and a gator who chomps his jaws a
little (ship and gator are fed with air bubble pumps).  I added driftwood and
dead coral rock (both of long ago tank use, saved and stored with the tank). 
We put in a few nice fabric sort of fake plants that look pretty real and
later will probably add a few real ones in among them.

            xxcarol
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