If you think it is a flushing issue try this (BTW I just had this issue on a buddies inside grow in a DWC, you could actually see the ssalt built up on the roots).
Empty your res, and or put the new one in place. Fill with R.O. water, set P.H. to 5.8-6.2. REMOVE YOUR RETURN LINE, and place it into a bucket. Run it for one day. Only problem I see with this is that in 15 minutes of "on" time, you will probably empty your res.. I will let you figure that one out. Maybe if you are around you can run 5 minute "cycles" manually.
Want to know when your flush is complete? Check your R.O. water PPM, mine is 35 for my home system, run a flush...remember our little "extra" res. inside our bato buckets? We gotta get that to turn over several times, while that is happening, and for a couple cycles afterwords, the roots will start to get cleaned off. End of day, take a water sample from your return line in a clean glass, not from the return catch bucket, but direct from the return line. If your ppm is above 50, you need to continue flushing. Remember the salts will not break down as fast as you think... kinda like concrete covering the roots.
nutrient lockout prevents the "good stuff" from being absorbed by the plant roots, that's why I suggested lowering your PPM down till the plants get stable. I agree with GPS, get some new
seeds started just in case, but all is not lost. I think you can bring these guys back! You also might be able to clone them, anyone know if you can clone tomato plants? That is if they are disease free.
Todd
Again, this is just what I would do in my garden...