New grow. 3 seedlings. a few questions.

In Advance I apologize, I took it upon myself to pen a lengthy post.

BACKGROUND:
I'm currently doing a closet grow. Aeroponic growtube built out of 6'' PVC tube with three sites meant for 4.5'' net pots, draining down to a 5 gallon bucket which serves as the reservoir. from there i have a 350GPH water pump irrigated via tubing exiting the reservoir, then going along the grow tube and ending with a ball valve. offshooting from the hose running alongside the growtube are 4 smaller hoses in which sprinklers are attached. these sprinklers are mounted upside down into the growtube - spraying the netpots from inside the tube.

the closet is 8' tall, 3.5' wide, 2' deep. approximately 56 cubic feet. walls, ceiling, and floor covered in a high quality greenhouse plastic - inside of the door and back wall covered with mylar. One of them nifty exhaust fans that are generally meant to be installed in bathrooms resides in the ceiling. I have a small HEPA filtration unit, as well as a cool mist evaporative humidifier running. Also, an oscillating fan coming from under the seedlings at an angle so that it's both directed at the plants as well at the 400wt light hood.

I have the room sealed up nearly as tight as a dolphin's sphincter. weatherstripping around the door, a threshold and door-sweep at the bottom - minimum light leakage.

sorry for the longwind about the set-up just thought it might aid in answering some of my questions.

QUESTIONS:
1) My most immediate concern is the temperture. According to my analog thermometers the temperture runs anywhere from low 90's to upper 90's. I have no air input other than whats being sucked from underneath the door. This obviously limits circulation. When I can, I leave the door open slightly to help with the circulation problem(s), though I fear this is unwise; wouldn't want unsuspecting eyes to glimpse.

(a) My question is how exactly does temperture correspond to optimized growing conditions? what risks am I putting the plants at by not alleviating this relatively high temperture?
- I know that the old watchword when it came to temperture was "If it's too hot for the back of your hand; then it's too hot for the plants."
When I do place my hand level with the plants it seems comfortably cool under the light. And, I've also took note in one the threads of someone saying that if you run your system then you can increase the humidity while simultaneously lowering the temperture. I've since done this and noticed positive results.

2) I'm now watching over three seedlings. I've planted the trio in three seperate standard dixie plastic beer cups, filled with a 50/50 of vermiculite and perlite. One of them is slightly older then the other two. It's an oddball. when it popped the soil, it only developed one cotyledon. It's also pretty leggy because the seedling had a tough time breaking the seed-shell, and I was reluctant to remove it forcibly until it was too late and it overextended. But it's not leafing correctly, I'm hoping it will literally grow out of it, but I'm not sure - is this something to be concerned about?

The other two seedlings are healthy and normal. two ctyledons, and currently two small serrated leaves.

(a) My concerns are for the leggy deformed sprout. should I keep up with it despite its deformity? It seems healthy otherwise, (nice and green) I'd hate to abort it just because it has a little personality.
(b)With one of the normal sprouts the cotyledons are yellowing, is this a bad thing? the serrated leaves are green-green-green, but the seed leaves are yellowing.

one last question, how high from the plants should I have my 400wt MH hood oriented? I think that the light is about 18'' to 2ft from the seedlings as of now.

If anyone actually labored through this post, I both apologized for its length and thank you for doing the labor. I would muchly appreciate any guidance, help, comments, et cetera.

Sorry no pictures. soon there will be.

One thing i can tell you is it is probably not a good idea to have that HID on those seedlings..how old are they agian? And for all your other questions i am sure someone will be able to give you some good advice...as i am new at this too....good luck tho man

I am no expert but i know the seed leaves (ctyledons) will yellow and die eventually as long as the other leaves are nice and green everything should be ok.
As for the dodgy seedling, i would keep it and see what happens you can always abort it later.

the dodgy one is about 2 weeks, the others around one week. I thought the HID wasn't the most ideal, but I haven't any fluoro's - so I raised up really high practically to the top of the closet, but I also thought that by doing that I'm significantly reducing the light intensity that's reaching the plants - which if I remember correctly operates on the inverse square law. meaning every 6 inches farther away the light(s) are from the plants there results in an exponential drop in luminous intensity. so that's 20,500 lumens at the point source, and as its distributed over more area the intensity is diluted.

I had my HID on my seedlings are someone on the forum (who is the shit) told me to get that off them seedlings...ive also been told that it stresses the plant alot and cause more hermies...CFLs work great and are really cheap..that is what i used until i got my 3-4node and then i put that HID on the ladies....hope this helps, just trying to help as i made this same mistake...peace out

helps plenty. I had suspected that it might be stressing them. you have any idea why, exactly, it does stress them?

from my understanding it is due just to the light intensity of the HID light...