They are there, trust me - usually by this point the ones with a commercial interest start to chime in about magic rays. I am very new to koi, but have been arguing with the pseudoscientists selling BHM since day one.
I notice by your low post count that you might be new here - you're probably lucky in that you have most likely missed a couple of VERY long threads on several boards, filled with lots of personal attacks, and lots of people who think they know science and have not a clue - all on the subject of bacteria house media. There are quite a few folks who advocate using a bakki shower as the ONLY filtration, whatsoever, anywhere in a pond. They claim you can pump from the bottom drain directly to the shower, and return to the pond - no form of solids removal at all, and have perfect water quality and fish that not only never die, but grant wishes and can fly. Ok maybe not the last parts, but those are just as much fantasy as the concept of solids "somehow" disappearing.
The real secret, as has been revealed in many cases, is that the design where only bakki showers are used includes one other key element - continuous water flow-through. That is, those solids that are pulverized into tiny bits by the bakki shower, get washed away with a constant 24/7 water change. Of course the zealots never acknowledge this point either, and claim the bakki shower is doing something mystical to the solids.