Trouble with German Johnson's

From the beginning, they seemed a bit weak in the system. I bought them as organic seedlings from Whole Foods. They just never seemed to take well to my aquaponics system, though they had 3 very large tomatoes (still green) on them. For the past week, they've looked weak and wilted, as if they weren't getting enough water. I tried giving them a little boost of nutrients, I tried pouring fresh water over their roots, and I tried cutting the water level down a little. Nothing - they remained wilted. I finally pulled them up yesterday, 'cause they simply didn't look like they were going to make it. The roots looked pretty rotten.

Doesn't make sense, as there are several other tomato plants in that same grow bed, and all are doing fine and producing fruit and looking healthy.

So, maybe it's just that German Johnson's don't do too well in aquaponics (or my aquaponics)? Or maybe I just had a couple of weak plants.

Will try them again next year to see if they consistently perform poorly in my system.