HELP! I have 6 thriving plants, One of them heavily drooping>please help

I bought 6 clones and they have been growing perfect. I have them all in 5 gallon pots under a 400watt light. All of the plants are grown in soil. All of the walls are covered in tin foil and the light is no closer ther 14-16 inches from the plants. I also constructed a wall that stands at a right angle to conceal the plants into the corner of my room. There is a fan on the inside to push all of the humidity up and out of the top. The only ventalation the plants have is a 2 by 4 window directly to the left of the wall. Recently I had to leave town and I have someone watching them. I got a phone call last night that my 5 week old sour deisel which was mi healthiest and tallest plant was drooping a little. I had a friend raise the light a little and asked him to let it dry out for a couple days. I call back this morning to see how its doing and my friend tells me its drooping even more. What is happening??? All of mi other plants are doing fine. I have a very healthy 2 1/2 foot super sour right next to the sour d that mysteriously started to droop. The leaves on the sour d are still dark just drooping. anyone know whats happening?

I was just told that some of the branches on my sour deisel are pink. What does this mean???? please help:(

i would think you need some nutrients

yes i think thats the problem through my self diagnosis. Phosphate or mg defiecency says leaves become dark green with purple, red, or yellow pigmentation with red stems. In this case they are a bit purple. Anyone let me know if I am wrong. Im on the way to the store to buy Kushy Kush right now.