With all do respect, I would advise against flushing organic soil. I would encourage you to read about cations, anions and cation exchange (CEC). Your base cations won't change from flushing. Doing so will merely leach out the most important elements for your plant during bloom, such as, phosphates and sulfates, etc.
Brown spots on lower leaves is most likely due to a watering issue, a pH anomaly, root rot, bugs or temp extremes. Could be a PK booster burn going on. Red stems and purplish hues suggest a phosphorus issue. The shade of green is a bit off. Red stems and dark spotting can also happen with N deficiency and if not corrected the stems turn black. But the spotting isn't black, so probably not N or Mn. Looks more like a P and K issue. K can be antagonistic to N, Ca, Mg, while P can be antagonistic to Ca, Fe and Mn which could, in part, explain the off coloration.
You are adding microbes so it's probably best to cut back on nute strength at least 50% and possibly more. When in doubt, start low and go slow. You can always add more, you can't add less, right?
Give her just water for awhile and see if she self-corrects before taking any drastic measures. These plants can handle a lot more than you might think. I strategically abuse them all the time to see what they can take. You'd be surprised. Lol
