Multiple Problems need help diagnosing and treating

I have a small soil grow going with all different strains, they are about 4 weeks into flowering, they are on 12on/12off a 600w HPS light, temp is around 70 during the day but i think it drops to almost 40 at night, but right now i have no way to up the temp unless you guys have some ideas, the first image is lemon haze and i cant tell if the leaf curl is over or under watering, or possibly nutrient burn, or a temp/humidity problem, the second image is raw diesel and it seems to have a nitrogen deficiency because of the light green color but i'm not sure, but there is leaf curl and dryness that i have no idea what it is from, the third is blue cheese and again i don't know what the problem is could be temp/humidity/nute burn/over or under watering i dont know, if you guys have any tips id really apreciate it!

whats the ph runoff?

i'm just watering with 7.0 water no nutes, the soil is testing aroun 6.25

you say 40 at nite,plants stop growing at 55,I have some plants that are about a week away from harvest and my temps are between 60 and 70 deg.with the lights on and my temps have been holding around 55 at lights out and alot of my leafs have turned almost purple due to the colder temps,I seen a osilating heater fan at walmart that I will be getting to keep my temp up,my grow room is in my basement and its winter now so it wont be getting any warmer down there

That is a pretty big temperature swing....whats your watering schedule like? are you allowing the soil to dry between waterings? if so how dry? they look pretty thirsty to me

I backed off on watering because the soil seemed to not be drying out, so now i dont water very often because the soil is wet but they seem to show signs of underwatering