Coco can be used hydroponically but it is not inert. Inert medias have no charge and are neutral like hydroton and rockwool. Coconut fiber is definitely organic matter with the same negative charge as other organic matter. There also seems to be confusion about calcium and magnesium’s relationship with coco. Calcium and magnesium are just 2 cations of 11 that can attach to negatively charged organic matter. Ammonium, potassium, calcium, magnesium, sodium, iron, manganese, copper, zinc, nickel and cobalt all will fight for space on a particle as well as harmful heavy metals like aluminum if available.