If you have built one and are running it, could you share your experience and what you consider to be the benefit based on your results?
i'm building one now and have read several articles about them; however the benefits seem to not be the same among articles. i get the idea that ammonia and nitrite will gas off from the fall and shock of impact on stone. another article that just came out says that we can reduce our nitrate levels. it suggests that the shock will reduce a nitrate to NO2 and carbon dioxide. that doesn't make sense from a chemistry perspective. the article also suggests building a moving bed filter with k-1 in the bottom tray. that doesn't sound like the original design.
the idea of fall and shock begs another question. how far must the water fall to provide enough energy in the shock of impact on stone to gas off waste chemicals?