davemonkey

Hi, Church!!

I think I'd go the El Natural route on this and use an organic potting soil mixed with some cheapie topsoil (or soil from your yard) , about a 70/30 mix (don't have to have that ratio, I'm just thinking CO2 from decomposing OM mixed with minerals in soil) and cap it with an inch of whatever you like (gravel, turface, aquasoil, sand).

This inspires me (except for the fact that I'm renting a house right now) to do something similar for an experiment station (to test "new" plants). You know, you could be completely natural with this. Light from the sun, filtration from plants, ferts from soil and fish waste (just like NPT), and if you need heat in winter, just throw up a small greenhouse structure over it (easy to do DIY on these) and BLAZAM, a large scale NPT.