New Grower: Curling leaves, what is causing this? (PICS!)

I have various bag-seed planted plants. They are grown in some "starter grow indoor plant" mixture from Lowes (it doesnt mention anywhere about having fertilizer in it or anything, it was the cheapest mix they had at the store). They are bring grown under four 6500k flouros, with a quiet humidifier bought at k-mart blowing air on them, and keeping the area in the 50-60% humidity range. The temperatures are typically between 74deg and 87deg, and are under the lights 24/7.

What is causing the lower leaves of these two plants to curl, and the other one to curl and droop? Additionally, I believe I'm noticing the ends of the bottom leaves go from green to a gradual yellow-color as it reaches the tip.

Am I not watering enough?

Plant #1 Angle #1:


Plant #1 Angle #2:


Plant #2:


OVerview:
http://imgur.com/4rTxm.jpg

87 degrees is hot. how old are they and how often are you watering. looks like overwatering to me. 24/0 light schedule might not be the best thing either. what's your Ph like? you need to give more information

im going to say overwatering, and ph is wrong

heat stress is my guess ... i have had some do that before from the heat

Heat stress for sure. The same exact thing is happening to me right now but not too horribly bad. Just turn the light schedule down to at least 18/6 and put a fan or 2 in there and you should be good. Good luck bro.