Fear the Dreaded Root Rot. Get some Serenade (Bacillus subtilis) in there right away if you've got it on hand, do a light mist with an anti-transpirant (Wilt-pruf, neem oil, SMC, etc but LIGHT is the key!!! Repeat if necessary but never to the point of runoff), raise your lights immediately. Your plants are losing water faster than they can replace it and you need to slow that down until the roots recover.
How is your res temp and oxygenation?
I'd also cut some chunks out of the bottom edges of the pots to improve drainage/oxygenation tothe roots.

Fixing rot is going to be a challenge. Treating with peroxide is a start, to kill the pathogens. This will also kill beneficials from the Serenade if you used it btw. Once the h2o2 treatment is complete, and you'll need to look up application rate or get a hydro person to answer that one, you'll want to run a Zyme to clear out the dead plant matter, and after a day or 2 change out your res COMPLETELY for fresh water, cleaning it as best you can.
stinkyattic Reviewed by stinkyattic on . plants r wilting 4th week flowering help stinky hey all, im in 4th week flowering all of a sudden plants started to wilt pretty bad roots look kinda brownish changed res yesterday using gh nutes 400 watt hps ph at 6.0 any ideas? Rating: 5