For an El Natural tank...
1wpg is not sufficient on its own - El Natural tanks make use of partial sunlight exposure.
1 inch of garden/top soil capped with 1 inch of gravel/sand is usually the substrate. Plain gravel or sand won't work. You should run a bottle test first to determine the nature of your soil (Test for ammonia and NitrIte release for at least two weeks). You can air/soak the soil to prepare it beforehand but do not boil it - the live bacteria are used to seed/cycle the tank.
Soil decomposition provides a carbon source initially, with mulm taking over as the tank matures.
Soil + Fish food/poop + water changes provide the plants with macro and micro ferts. You only dose small amounts if a deficiency appears (e.g. I dose potassium)
Maintenance is easy. You top off evaporated water and only do a 50% water change every 6 months or so. Gravel vacuuming should be kept to a minimum or not done at all so that mulm builds up.
The plants act as the filter, but you still need reasonable water circulation for this to work (and you need this from setup). If you have fish you want to immediately re-home back into an El Natural tank I would keep a mature filter running for two months and gradually remove the filter media.
You need to match your fish load to this regime. The planting needs to be on the heavy side, with some fast growers present, and preferably some emergent growth.
This is the essence but its open to modification to suit your situation.
For further info try getting hold of a copy of "Ecology of the Planted Aquarium" by Diana Walstad, or visit the El Natural forum on Aquatic Plant Central where Diana is a moderator.
Good luck
