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.