yellow spots, mag deficiency?

I just read the post below this one of what seems to be the same problem. but not wanting to hijack his thread Im making a new one.

I have 19 lowryders in a closet grow with cfl's and HPS's. they are about 3 weeks old. I am growing in ocean farm soil and have added NO nutes. i water with filtered tap water that sits out a bit. but my ph's can be a little fluctuating because the biggest pot i have is like 2 gallons. so I try to keep the ph the same but of course i cant match it perfectly. and its a color chart so its even worse.

alot of the plants leaves feel a little stiff...but this is my first grow and im not sure how they are supposed to feel. the ends of some are also curling down just slightly. and this plant just started showing these small yellow spots. any opinions? thanks guys!

oh also. the temp and humidity vary GREATLY! if i open the door the humidity drops like 20%.

with hps and cfls on and humidifier running the temp runs 100 and the humidity runs 90%!
so i leave the door open when the clf's and the humidifier are on.

with just hps's on the humidity is about 80% and temps are about 80.

what i try to do is let the cfl's and humidifier run till the room is nice and moist and wamr. then empty a co2 cartridge in there and cut the cfl's and humidifier off. and just let them soak in co2 and hps light.

Check this post it might clear your doubts:

https://www.rollitup.org/marijuana-plant-problems/132382-deficency-nute-burn-diagnostic.html

thanks a lot! that's very helpful but unfortunately I don't see anything that resembles my problem. just tiny yellow spots on the leaves. also I just opened my closet this morning and they've been under 4 hours of light without having watered today. 80 temp and 60% moisture. and they are droopy and the leaves are curled up? heres a picture...

here. the drooping is prolly just wanting water. So I decided to water them and flush tomorrow. then ill start with quarter strength nutes.
looking in the closet they already look perkier but for now the leaves still curl up..

http://www.icmag.com/ic/showthread.php?t=11688 check out this guide brother...also.spider mites will put spots that look like that on the leaf's of your plant..make sure there are no little spider webs anywhere around your leaf's and no little creeping critter's running around on your plant..good luck..