OG KUSH CBD photoperiod. first grow!

noticed an older bigger leaf is showing some sort of issue- cannot find online. i believe its a mag-deficiency. worried about the plant drooping a tad. unsure if i am feeding enough. still learning. also not pictured: the plant has been topped, and has some LST. i am insecure about these techniques- i believe i did this wrong as it doesnt seem to make sense to top AND do LST at the same time- counter productive. Sprayed the plant with 'Garden Basics- Insect and Pest Spray' as a preventative- 10/10/21