Hydroponic mediums, moss, coco, perlite, hardened expanded clay, vermiculite, rockwool and neoprene discs, are some of our non-organic mediums or non-mineral soils, used in hydroponics, the difference between soil and non-soil mediums is their ability to hold water and oxygen, and their ability to hold onto nutrient ions and supply them to the plant roots as the plants call for them. (CEC) Cation exchange capacity is the ability of a growing medium to hold nutrients on call for the roots to uptake. The CEC of each medium will affect the pH for maximum nutrient uptake.
Regular dirt soils with their particle charges electrically hold nutrients readily available for the roots. they have high CECs between 100-200 equivalent units. Vermiculite and peat moss mixes have CECs of 50-60 equivalent units. Rockwool, perlite, and water cultures have a CEC of 0 they do not hold nutrients on call for the roots to uptake, and once a nutrient has passed by, it is gone. it also means that these mediums have no buffering effect.