over time the small pores that provide the large amount of surface area can get clogged, so that the surface area for the biofilter to live in is reduced. Always have mechanical filtering before the ceramic biofilter. Never remove it all at once, probably should never remove more than half. I've heard rinsing works well, but soonor or later I would think it should be replaced. Why not add some new stuff on top of the old stuff every 6 mos, when the compartment is full, get rid of the bottom layer to make room for the new stuff. This way you would be stretching out the life of the ceramic, and would never remove too much at a time. I think the manufacturer has good practice in mind, but boosting sales is probably a motivation too.