Help MAN DOWN. Week 7 of Flowering

I believe this is a phosphorus deficiency. Strawberry fields soil till soil nutes ran out. 5 gallon pots. i noticed 2 fungus gnats stuck to two colas so i fed twice every other day root cleaner. Cyco nutrients suggest 5.5-5.8 for soil. I changed it to 6.2 week 6. My other plants in week 3 are starting to show shades of purple. At night the temp goes down to 60-65 but no less than 60. ppms at first were 1200 per instructions but figuring it was cookies i dropped it to 1000. My gorilla glues and gelatos aren't turning purple but are fairly smaller after you guys help me with this i can show pics of those. No mites no pm. No overwatering. sometimes they wilt just a bit on the other day of feeding at night Before i feed But not full on wilt. Also the leaves at the bottom end up turning brown and dying at the very bottom of the plant under the net.

Phosphorous IMO.

Cooler rootzone temps can restrict phosphorous uptake.

pH should be at 6.5 - 6.8 for soil grows.

Some strains genetically turn purple in later flowering.

(Just realized this post is nearly a month old LoL)