aqua_chem
Aquarium Advice Addict
Someone made the comment that scientific experiments weren't necessary.. but IMO, to get a definitive answer on most of the questions brought up, they are. One can only speculate that most bacteria live in the filter in the majority of tanks. I can tell you that I've got two tanks running with no filter media. One is lightly stocked with only a bristlenose and 4 otos (29g). The other is a 150g that's pretty heavily stocked. Both are planted. Both only have mechanical filtration that's replaced (not rinsed) every week or two. I've yet to detect any ammonia or nitrite, and very very little nitrate in either tank. This leads me to the suggestion that bacteria will make themselves a home wherever necessary... I don't know all the science behind the various types of bacteria, whether they are free swimming or not, etc etc... I do know that what I've done has worked for me (for 4 months now... not a big acheivement, but promising.
FWIW, I did it as a test and it worked. I tried on a smaller scale first, and it worked.
I would credit your plants before I credited the bacteria. The low nitrate attests to that.