New Grower My 3rd grow 6 dinafem critical jack 3 sweet seeds red poison

[WeeDnWinE]

i have just joined, i have a few critical j's at 5 weeks and they look identical to your 5 week pic, recently tho i have noticed the stems leading to the fan leaves r turning purple? i had a cool air feed entering the bottom of my tent from outside, could this be from the cooler temperatures at night recently in my area? or are my plants lacking somthing? also should i be giving them neuts, all my previous strains have been fine with neuts but i have give my cj's biobizz bio grow and bio bloom and some of the fan leaves have turned yellow and the ones at the bottom have died, even tho i used not even half the reccomended dose?