David, I just went to a research facility last week where they're trying to figure out WHY aquaponics is so much better than hydroponics or conventional gardening. One thing they're hypothesizing is that a few of the microbes present in a living system facilitate sodium uptake by plants - some tomatoes they measured had over 10x more sodium in their roots and stem than in other systems. In hydroponics, this isn't the case, and nutrient solutions have to be dumped from time to time. The water in their aquaponics system is quite balanced and they claim to only be adding dechlorinated tap water for evaporation top-off.