Dry Rock Suppliers

[FitoPharmer]

Uhh I am sure I can dig it up. But I think somewhere the point was lost.

The area 1-4" beneath the surface has enough oxygen to harbor the bacteria that convert ammonia and nitrite. Rock that is dense enough or porous and large will have an anoxic zone in the center where nitrates are converted into nitrogen gas.

And yes if you have sufficient surface area in your tank covered in bacteria, that will act as a bio filter. That is the whole point of bio balls.