The big leaves are dry and break toward the end. Didn't expect things to progress that quickly.
One thing of note: I had a long work day and the humidifier ran out of water. They probably went several hours at 30pct humidity and saw a max of 80 deg F. The other plants are just fine.
Edit: one last thing: I did top yesterday, including both affected plants!
Have not fed anything yet. They have been in new FFOF and recently up-potted. This was even present to a minor degree when they bad one was still in it's starter container:
(Note the bottom most leaves -- this was 4 days ago)
Not sitting in still water
After searching specifically for phosphorus deficiency, that is a definite possibility. I have fox farm Big Bloom bat guano & worm casting liquid; I'll try adding it at a high concentration next watering.
I searched for P Deficiency & how to address. Online sources say to add worm castings/guano. I thought I had some of this extra, but no. Another method is add high P fertilizer or super phosphate or something. Unfortunately money tight right now, as per usual.
The two previous plants are the same but maybe a little worse. As of yesterday my 2 other clean plants are showing the same symptoms:
Please see my journal linked in OP for complete timeline.
I gave the 2 worst plants from first post just a taste of bloom fert 2-8-4 at night, then the next evening fed all 4 with 0.5 tsp/gal veg fert 6-4-4 two days ago. Nothing dramatic since, but this blight does develop rapidly.
I am starting to see root tips poke out the bottom of these pots' drain holes and will transplant to 3 gal as soon as I can afford new dirt.