Upper plant leaves edges are starting to turn purple. Lower leaves r rusting over.

12 weeks in on plant. Coco coir grow. 2.1.1 nutrient ratio because started feeding at 10 weeks. Major lighting issues during plants young life. Fixed issues by upgrading from 15 watt led to 300 which cause the plant to have a beautiful bloom. Just noticed although, some slight early damage to the lower fan leaves that i have no idea what could be causing. Usual decaying of lower leaves. But also an alarming early redding of the sugarleaves leaftips of nugs on the cola has also suddenly appeared. I am lost as the lower fan leaves look as if their nutrient burnt but the upper leaves could possibly have a nutrient deficiency . Or a possible even major burn as the plant was 12 inches from the light, It seems to flourish at that distance although. If someone could please help me with these couple small issues i would greatly appreciate it. Just fed plant a 3-2-1 nutrient ratio to fight a phosphorus deficiency, but this feeding has caused a sudden drooping of leaves. So mayb a phosphorus lockout?

Just also found out that my room temperature dropped to 66 degrees when curling started.