I know what thread you're talking about, and what he's got going seems to be twofold at the beginning of his new cartridge. I'm willing to bet dollars to doughnuts that after 1-2 weeks the carbon becomes too saturated to perform any chemical filtration and at that point only serves as a biological media, becoming housing for the benthic nitrifiers.
Nitrifiers are bacteria that oxidize wastes, starting with ammonia, and ending up with nitrate in an aerobic-only system. If there is a low-flow anaerobic filtration area (aka denitrifyer), then the nitrates are further broken down and the N is sent back into the atmosphere. Denitrifying filters must be handled carefully or a system can be quickly killed.
In any event, our other friend over there is using a cheap hang-on-tank box power filter. What he's getting from any NH4 that's being processed is ultimately NO3. The sequence is NH4 --> NO2 --> NO3 (in an aerobic environment).