Do not feed seedlings that little anything. I think it is a mistake to start them in 5 gal containers. It is too hard to control the water to the seedling. Also, that soil mixture just does not look good to me--coarse and barky with no perlite. I am a water baby, so maybe one of the dirt people will chime in.
If the red thing i the dirt is one of those pH/moisture meters, I would get rid of it. IMO, they are worse than useless.
i started all of them out in small cups but they quickly outgrew the cups... i was using several 400 watt Halogen bulbs but they got way too hot...so instead i switched from those to about 6 CFLS. The plants in a box that is about 2x4x6 and is ventilted with a fan. the edges of the box are lined with Mylar. do you think its possible that the mylar is maybe working against the plants?