I have read it can deplete O2 also. Where do you get your info?
All bacteria in a closed system involving a recurrent bio load will use disolved oxygen.
Aeration will not increase oxygen levels in water just by bubbling bubbles up through the water column. The bubbles breaking the surface, essentially "stretching" the surface of the water exposes more water to the atmosphere to affect the natural gas exchange. The only way to increase oxygen in water is to: A, rapid exposure of as much water as possible to the air through turbulent movement or B, actually subjecting the water to pressurized O2 infusion at a microscopic level.
The minor movement acheived by adding an air stone may increase O2 levels, but only because the depleted water in the lower regions of the water column is being moved to the surface.
The reason oxygen is reduced in a bio-media treated water, and maybe its a surprise to people who have had inadequate bio filtration, is because of the growth of benificial bacteria.
Now, K1 is an efficient and effective bio-media, but it isn't doing anything new that other media isn't doing other than the "knocking off" of heavier older bacteria throught the movement allowing new, more inergetic bacteria to colonize....
My info is gleaned from years in school and a decade as a waste water plant operator. The science is very easy to understand, and the process is very simple and easy to learn about.
Before K1 was around, fluidized sand bed filtration was all the rage. In fact, and I will stand firm in this, fluidized sand has way more surface area then K1 could ever possibly have. Scintered glass and ceramic foam media far out performs any non-porus media pound for pound for available surface area colonization.