It isn't that porous, and I think the denitification potential of live
rock is usually overestimated. It is variable. It also might be
difficult to find appropriately porous rocks for a freshwater tank that
were not made of calcium carbonate.
> The second "filter" that comes to mind is a Jaubert setup which is
> another denitrifier used in SW tanks.
That does work. Which is why I suggested a deep bed of coarsish gravel
for fishtanks. The gravel in our freshwater tank always has gas bubbles
in it, which I presume are mainly nitrogen.
One caveat that you should be aware of... when denitrification is going
ina system, there is generally some nitrite around. That isn't a big
deal in marine systems, since Cl- competes with NO2- for uptake.
However, it might be a very big deal for freshwater systems.
Craig