Pls help me, Black spots on leaves, purple stems, curling leaves

[Chozee97]

Good day,
I'm try outdoor grow for the first time, 4 plants in 20l pots.
About 14 days ago, I accidentally gave the plants fertilizer with PH 8.0 ("ph meter died") , after that i flush with PH 4.0. After 3 days i watered them with PH 6.0.
Today is 14 days since I last fertilizer and yesterday I found purple stems and a few dark spots on all 4 plants on the leaves ..
This afternoon there are dark spots on all the leaves and the leaves are curling upwards.
Would anyone please advise me?

 

[Pushrod Monkey]

Is that powdery mildew in the last picture?

 

[Chozee97]

Is that powdery mildew in the last picture?

No

 

[mancorn]

Spraying in the sun? Helps if you give more info or it’s just a guessing game. If you’re in soil, your feed pH isn’t a big deal and not what is causing the problems.

 

[Pushrod Monkey]

I see phosphorus deficiency. You’re sure the white on the leaves doesn’t just wipe off like dust or powder?