Basically it's a very low tech set-up that Diana Walstad published in "The Ecology of the Planted Aquarium". In essence you use potting soil with a layer of gravel over top and then heavily plant the tank in that. The plants handle all the filtration etc. Water changes can be done every few months.
Here's a step by step thread on setting up one of these tanks. And
this is a thread with actual discussion on how to go about doing an el natural aquarium. I'm currently waiting for my local bookstore to order in my copy of her book from what I've read it's an interesting read. Basically el natural is a no tech tank, using sunlight and ambient room light. I like some idea's on it but some I'm not a big supporter of. Such as the sulight only and the no water changes. Water evaporates and leaves the salts behind and I have to top my tank up at least once a week due to evap. the residue build-ups in the water (and my water is hard to begin with) just isn't something I want to deal with. And I'll stick with my hood light and heater instaed of the sun. I've read to much about sunlight cooking tanks to try it.
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wow that was a ramble hoped it made sense.
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