I'm not entirely convinced that more surface area always translates into more effective filtration.
One consideration is internal versus external surface area. Expanded ceramic and glass media have such a (nominally) high surface area because it is calculated by considering the total surface area of the media's internal structure. If a layer of bio-film coats a nodule (which will eventually happen unless I'm missing something) then water will not flow through the interior, effectively reducing the surface area to that of the exterior.
One consideration is internal versus external surface area. Expanded ceramic and glass media have such a (nominally) high surface area because it is calculated by considering the total surface area of the media's internal structure. If a layer of bio-film coats a nodule (which will eventually happen unless I'm missing something) then water will not flow through the interior, effectively reducing the surface area to that of the exterior.
