HYDROPONICS is a system of soiless growing. In other words nutrients are not in the medium, but in the water. So of course there's soiless medium such as clay pebbles such as hydroton, there's rockwool as well as coco and others. The point is they are mainly there to support the plant, not to feed the plant. Depending on the medium, a watering schedule needs to be used. Hydroton does not absorb water (nutrients) as well as rockwool, so in order not 'drown' them, you would not run you E/F system as often using rockwool.

As far as soil is concerned, I suppose you could water your plants using the E/F, but what would be the point? Your nutrients are in the soil, not in the water. So you would have a glorified watering system for your plants growing in soil. A system such as that would at the very least wash some of the soil back into your water, and may start plugging pumps, drains etc.

keylime