Been through this before with her bro, do you mean bananas?
The h2o2 is a good idea mate if heat is a factor, how are the roots looking. That's the reason I dropped dedicated hydro. I was close to buying a chiller for the multiple res's, I found a way to daisy chain and cool all the res's with 1 chiller, it's on RIU axtually where I got the idea. The temps where I am fluctuate to the extremes.
There should be plenty of cal/mag in your nutes and tap water but I know the kushes can be calmag hogs, how are the roots? Maybe bump her back down and raise slowly, if the ppms are high she could be locking out. How about hitting her with a foliar feed/tonic, kelp or compost/worm juice, I know it's hydro but a light foliar will perk her up I bet.
Peace mate.