Well you mentioned the ph was rising (this is consistent with nuteburn) and now dropping (consistent with roots dying off). See how it works?

You know I just flushed one of my plants and think I wrote down the way I do it. If you are not using a zyme product I would add hydrogen peroxide to your water at the rate of 2 teaspoons (10ml) per gallon of 3% store bought peroxide every other day OR if you use the hydro H202 (35%) it's 2 ml/gallon every othe day. I'm assuming you aren't running something like cannazym or hydrozyme in your res along with your nutes.

The H202 is to try and add extra oxygen along with killing off some of the germs and bacteria in your roots and medium.