Oh and I use bio balls and have nothing bad to say about them
Yeah, maybe I went a little overboard on the "there can be no pro-bio-ball argument" lol. I used bio balls in the beginning, and up to the point when I concluded they're a waste of space compared to the other media available.
I'm not a biologist, but the nitrogen cycle interests me and understanding it is important to keeping fish alive.
As far as the reference, again, that's just not how it works. Nitrifying bacteria reproduce by binary division, meaning each cell splits into two new cells, and this happens about once every 10-20 hours, so there's no such thing as "dying of weak old age". In the aquarium, assuming stable temperature/PH/oxygen, bacteria die from lack of food (1. They've completely consumed available nutrients, which is exactly what we want them to do; or 2. They're smothered/starved by the new bacteria growing on top of themselves).
So, in the case of a reactor, I believe you would actually be knocking off the new (what could be called "strong") bacteria at the surface of the colony in order feed/sustain the starving/smothered bacteria cells underneath, which is fine. The dead bacteria at the bottom are a bunch of dudes who simply didn't get a chance to eat.
