I admitedly haven't read the entire thread, but I will when I get the time. This type of system has been used in agriculture/aquaculture for some time now. It is called an aquaponic system. There are many ways to set it up and lots of information out there about it. Tilapia, baramundi, catfish, perch, etc are rased at high densities in these systems with no ill effects. Water changes in their minds are lost nutrients for plants and they are typically not done. You would lose water through evaporation/transporation that would need to be topped off which would replace most of your salts and carbonates. Try food plants like herbs and lettuce, you just may have to alter the setup of your planted section. I have to ready to educate the youth, but there is a lot more I would like to share later.