The other day I picked up the book titled "Eating on the Wild Side" by Jo Robinson. It's a fascinating book. It tells of the history of fruits and veggies, and how we've changed them over time to appease our taste buds. She also goes over what phytonutrients each plant has, then breaks down organic vs conventional on some. Which got me thinking... has there been any studies on the differences of the nutrients/phytonutrients between organic soil grown veggies and aquaponic grown? I would think that it would be similar, at least with the plants growing above the media since they would create the phytonutrients to protect themselves from the sun like soil grown, but what about a root crop? Like carrots and turnips, things like that. Would their constant flooding, or if it's possible to raft grown them the constant soaking leech the phytonutrients? Mostly this is for my curiosity. I grown both with aqauponics and organic soil so it doesn't really matter all that much, just some thoughts. I definitely recommend this book though, I'm having a hard time putting it down and my wish list for heirloom seeds is getting bigger after every chapter.
Plants don't leach essential nutrients. If they did, it means they're dying and decomposing. That's like asking if people leach blood when they sit in the bath or swim for too long! ;) Plants are not the porous open-to-the-environment sponges some people think. They actually have a sophisticated anatomy of cell walls and transport vessels that they vigorously maintain in order to separate and protect themselves from the environment.
That doesn't answer your question, but I wanted to clarify this part of the issue at least.