Jeremy has some good points, ...
Published by Gerd Teunissen, technical director at INTERAGUA, Lda.
Jeremy has some good points, but I don't understand Guy McGowen's observations in this context. Random packed media will create not flushed pockets, with all the consequences, mainly loss of effective surface and anaerobic conditions. Higher specific surface, also for structured media, reduces the free passage and increases the clogging risks.
An interesting option, absolutely clog-free (!) and with high flexibility in m2/m3 variation are the SESSIL® film strips from NSW (Germany).