Substrate vs water column

Dear Folks, 

		I have recently set up a 20 G long with a vermiculite/soil/
worm castings substrate covered with a couple of inches of gravel.  I do 
20-30 % water changes every other week with ph 7.5 water and have a DIY 
CO2 infusion setup that keeps the water ph below 7.0.  My question:  Is 
the substrate enough fertilizer for the plants or do I also need to 
supplement with fertilizer in the water column?  I have heard that a 
fertile substrate can provide all needed nutrients to the plants through 
thier roots.  I am not talking about hard to grow plants here.  Vals. two 
E. species swords, bacopa, cabomba sp?  h. polysperma, ludwigia, 
sagittaria and anubias nana.  What do people think?


					Miles Morrissey
					mmorriss at sophia_smith.edu