my babies x20!!

can anyone tell me what might be wrong with my babies?

400w cooled hips.
0.25l of water every 2 days.
75-82 degrees F (day) 65 degrees F (night)
humidity 30-40%
the room is well ventilated.

i just fed them (20-20-20)... might that be the problem? they'v been potted for 3 weeks now tho, i figured it's time for a feed and i didnt put too much in, i followed the manufacturers recommendations...

the first picture is the worst of the lot, but the same brown tips have appeared on all my plants....

You shouldn't have that much of a temp variance though it's stressing your plants as well as you might be overfeeding

yeah i thought about that being the problem, but really i cant do anything about it, the light gets HOT and i cant do any modifications to the room for like ventilation, all i can do is put an oscillating fan on the plants and open the door, but that's not a problem for me, i like the smell the temp is really a bit more steady than i made out now, it's 75 day, 65 night. they get a dose of CO2 every night as well.

what food numbers would you recommend for veg stages? is it mainly just nitrogen im after at this point?

might there just be not enough space?