Is this a deficiency or some disease? (pics)

I need help in identifying the issue.
Growing NL auto from seedsman since 7 weeks now. Noticed black spots on leaves and yellowing. From a google search, it appears to be any of the following

1. Potassium deficiency
2. Mag deficiency
3. Underwatering
4. Incorrect water ph (i've been using 6.5 to 6.8 ph)
5. Disease

Experienced growers, please advise me on what the issues could be. Can it be solved or is she a goner?

Here is the setup

1. Medium: Soil-less mix (coco, vermicompost, perlite)
2. 200 W full spectrum LED
3. Temps: 27 degrees in light, 25 in dark; 18/6 cycle. Humidity: 40 to 60. 2x2 grow tent
4. Age: 7 weeks since sprout
5. Pot size: 5 gallon fabric grow bag
6. Nutrients: Supersoil technique with autoflower living soil concentrate in potting mix; 2 tablespoons of "girl power bud booster" top dressing/4th day since flower

More close up pics

My guess would be the Aids virus, or Ph

looks like classic K def
not sure what the correct ph is for soiless but yours seems too high
also could be feeding too little K or K is getting locked out by overfeeding of something else, too much Ca for example would lock out K

Im leaning tword what yosim is saying.. looks like potasium deficientcy or a mag issue..

Adding some more pics of the leaves whose closeup I had taken.

I did a flush with 6.5 and the runoff was 5.4.. I did another flush and the runoff is now 6.8 or so.. is that a good sign?
I also feel its not a fungus, though one of the closeups has some white spots.. any clue what they are?

Adding pic another leaf that I tore off to inspect closely. I feel its due to pH lockout.