What is wrong with gravel. I use it in my tank and my plants are great.
Most aquatic plants get there nutrition through their leaves anyways so
the other stuff is a waist of money in my opinion. The plants roots are
more or less anchors for the plants and good water movement through
their roots is another good benefit from gravel. And lastly if you use
a good fertilizer and have fish to provide nutrients, the substrate is
not very important.

Vicki

my 2 cent