Deficiency or normal draining of nutes?

So I’m having some issues with my flowering girl right now.
At first I thought it was N deficiency but after testing the soil it’s full of nitrogen.
Then I thought it was lockout so I flushed and still after a few weeks she’s still showing these signs of illness
Can anyone help here?

promix BX
PH 6.1
Ppm 900-1000
Feed - feed - water

Poor watering practice...
Over fert for small plant
Pot too small... drying out fast?
And it's been hot.
Can't tell you exactly what's going on but I'd look closer into these ideas.
Also once the leaves are damaged they won't come back to normal. They'll always be necrotic. Keep an eye on new growth or new problems on other old leaves