Sit in your room with the doors shut and all the lights off. After 2 minutes can you see your hand in front of your face? If so, you have light leaks. I use Great Stuff to seal them. Straight 12/12, no weird lighting schedule. Switch to bloom fertilizer the day you flip the switch, no need to continue giving grow formula, your plant should have plenty of N to support it during the stretch. If it DOES start to show an N deficiency, just back off on the bloom and give it some half-strength grow. Beware of the stretch, most strains double in size the first 2 weeks of flowering; some strains triple in height. Make sure the plant is in the pot you want it in, transplanting during flower is not favorable. GOOD LUCK!