Dried Leaves, Lockout or Stress. Week 5 of Flower

It seems like potassium or magnesium deficiency, more likely the former.

how often do you water? And how much?

how many days do you have left? You should probably stop fertilizing now!!!! Just give it enzymes and water

Did no one notice those roots???!!! You're advising here like this the substrate is dry as a bone if the roots are supposed to be in the dark, then make sure to add substrate and cover those roots, ideally fill the container so that the roots aren't visible!!!!!

less than 68F - gd won't display the "less than" symbol.

No, those are advanced symptoms of one or more nutritional problems. looks like it paled bottom-up? If that was the progression, low-N. May have more than one thing going on. probably* have more than 1 thing going on. Need to see how it progresses to better diagnose. The reds and purples are probably 'Fall' colors and/or cold temps ( 68F ) FWIW: coco - 33% of volume shoudl be perlite or similar sphagnum peat moss or 'soil' should be 50% That is not the problem here. It may have impacted overall growth rate, but not causing what you see. Watering is simple 1) fully saturate (if soilless, religiously get 10% runoff or more) 2) wait for appropriate dryback and repeat You cannot drown roots or overwater by following basic practices.

Nutrient salt toxicity from not getting decent run off each time you irrigate? Nothing to do with oxygen levels.