I love the concept of aquaponics! I read about a guy growing this way and he had a two tier medium set up. The top tier holding soil or coco, can't remember which, and the lower tier being flood and drain. It meant he could supplement the nitrates if needed. He had it so dialed in that he knew how much he could pour into the top tier without it dripping down.
I think anyway... shit, I'm going to have to find that article!