My 600W Nirvana Mystery Seeds

Hey guys, so this is my first grow, looking for some advice. These pups vegged for 5 weeks, and just completed their second week of flower, and they're lookin cranky. I only watered (no nutes) until the 1-month mark cause they were in FFOF soil. I then introduced 1/4 strength of fox farm grow big, then plain water, then 1/2 strength. After a week of flower, i introduced 1/4 strength tiger bloom. I also use 1/2 strength big bloom with every watering. I think the grow big may have caused this, but a lot of the lower leaves are curling down and the upper leaves are shiny/dehydrated-looking/yellowing tips. The humidity stays around 40-50 during the day, but I turn the dehumidifier off at night cuz its kinda loud so humidity spikes to around 70 at night. I water every 3-4 days and alternate feeding (water/feed/water/feed). I'm thinking i'll hold off on the feeding for a few waters and see if they improve. Let me know what you guys think, and please refer to pictures as (1), (2), etc from left to right. Thanks!

more info:
-600w hps
-65F night - 80F day
-i use pH test strips wihch are hard to read accurately, but it seems like pH is ~6
-oscillating fan runs throughout daylight cycle, and on/off in increments of 30 minutes at night

-these are all free seeds from Nirvana, can anyone identify the strain of any of them? (I know it's probably too early with these, but I will post more photos as they mature)

Just finished their 4th week of flower, what's wrong with em?

yellowing leaves with growing brown spots on fan leaves of two of them (predominantly on bottom of plant, but carries throughout to top)
and purpling tops of stems on the same two plants

also, can anyone identify any of the strains? (Nirvana freebies)

Thanks!

bump... anyone??

somebody help me