Microbe life

[Steviestash]

I guess it's better with coco

 

[KonopCh]

With "hydro nutrients", which are already dissolved and pure, you don't need microbes. NPK can't go on any smaller particles, NPK is ready to use.
However, organic matter is different story (think about manure). Then microbes comes into play, they break down this shit. Literally.