Ammonium And Bacteria In The Fish Tank

[Kaidonni]

I remember TwoTankAmin once posting in a thread of mine - at least I think it was one of mine - some information on research and links regarding the metabolism of ammonium by bacteria in fish tanks, and that the bacteria that do this don't usually occur in most filters. Does anybody remember that thread, or have any idea what I'm talking about? I'd message TwoTankAmin, but it looks like he hasn't been active since the start of September, so I might not get any reply.
 
Note that I am talking about ammonium rather than ammonia - I tried a quick Google search, and the darned thing insists on giving me results about ammonia...
 
Thanks.