This is a common misconception about aquaponics. I have grown just about any vegetable you can imagine with the aquaponic system I have here in SC. You can see photo's of what I have grown at the photo gallery of my website
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Most people who have pretty much done only aquaculture or hydroponics, for some reason or other, can't quite get thier heads wrapped around this. Yes some fish are more sensitive to pH than others but good choices of fish can make all the difference in an aquaponics setup. I have grass carp, koi, and tilapia in mine and they do quite nicely. The aquaponics feature can even allow higher stocking densities than standard aquaculture without the pollution potential and constant partial water changes (I have even had over 700 1/2lb fish in a 1000 gallon system). The only water I add is from evaporation/transporation. There are some limitations but not nearly as much as one would think.
Trav.