Someone else posted pics of the exact same problem- chocolate-colored spots- and I couldn't quite place it either. My suspicion is fungus but that's not a diagnosis by any stretch.
What I DO see is a multi-nute deficiency starting with Magnesium and Nitrogen, plus enough tip scorch to make me think LOCKOUT.
You are likely due for a flush, and I'd suggest adding some Serenade (bacillus subtilis) to the final flush to guard against fungal infection in the root zone.
Your nute cocktail is pretty crazy- that's a lot of stuff going into your nute solution. One thing that sticks out is that you are using 2 different 'thrives' which you should never do. They are already so easy to OD on that doubling up is just begging for trouble. Never use more than one drop per gallon of the superthrive in your normal feeding schedule.
I'd cut way back- strip your nutes down to the bare minimum of a complete grow fertilizer with no thrive, and the silica blast ( I think you can apply this as a foliar, and I'd do that since your soil is already in need of a flush), but go real easy on it. Something is getting locked out and the plant's immune system appears to be suffering as a result.

Edit:
Dude. That can NOT be Ronald Reagan... but it appears to be... EEP!
stinkyattic Reviewed by stinkyattic on . Problems in Soiless My grow is: Indoor,soilless,Sunshine mix #4 and #2. Nutes I have and use consist of: Super thrive 1-1-1 Earth juice grow Silica blast tiger bloom 2-8-4 Rating: 5