One of my seedlings is a few days older than the other four, and is turning yellow. I've got 5 Low Life Hindu Kush seedlings in a ~1.5'x1.5'x1.5' grow box (with fan), with 2 26W 6500K CFLs. The temp is 75-78F in light, ~69F in dark. Light is on/off 20/4. Soil is composed of mushroom compost and perilite. No nutes. The first one was started before I had the box, and any way of measuring the temp, so I had a hanging light with foil around the light and seedling, with some holes. Might have gotten too hot for a night. It has grown since it was put in the grow box, but keeps getting yellower every day. I thought it might gotten over watered, but when I went to mix more perilite in the soil, I noticed the roots looked good. Whats goin on??