White Widow - My First Grow

Start of the week ================ Started flowering this week but there were signs of pre-flower last week. Began using flower nutes and started seeing signs of a deficiency in the lower parts of the plant a few days later. Believed to be an N deficiency but I've taken to reddit to ask for advice. The main stem has gotten really tall now. Lesson learned on managing light better. Because its grown so tall I've had to re-jig my lights to allow for the extra growth and a 18-20 inch gap to my lights to prevent stress + burn. But been dabbling with the brightness to keep a 30kLux brightness on the canopy. Noticed I had quite a few bud sites that weren't really getting much light and were hugging the main stem. I never really wanted to do any LST for my first grow, but decided to dabble with it a little to try and maximise lighting to those sites. Also trying a little LST with the main stem but unfortunately its all a bit late for that now. The stem is pretty big and feel I risk snapping it if I try too hard. Not confident enough yet to super crop either, and its flowering now anyway so don't think I should start messing around. End of the week =========== After heading to reddit to ask some questions regarding what I thought was Nitrogen deficiency, I've since decided it might have been a magnesium deficiency and also that I may have been under watering. I've always sided on caution when watering to not water too much as overwatering seemed to be a common issue. Decided to increase nutes, add some epsom salts and give the plant a good watering till I got a fair amount of run off. I felt this may have over watered the plant massively but it didn't show any signs of that. It was also he first time I've properly had the opportunity to PH the runoff and it was around 6.8PH, so the next watering was slightly reduced PH. The damaged leaves won't recover so I decided to trim them so I could keep an eye on progression of the deficiency. Turns out theres still a bit of an issue at the end of the week. See photos. Also removed the LST as the plant has slowed its growth.