IMO the soil you are using is not good for starting seeds....you need a lightweight that does not hinder root growth....something like Hoffmans Seed Starting Mix or Jiffy Seed Starting Mix or Light Warrior...these are very light weight soil-less mixes...plus the fact that the miricle grow contains nutrients and may be too hot for your seedlings...may be burning them up before they get a chance to get started...your one goal when starting seeds is to get good rootball development...a healthy rootball means a healthy plant...
I know a lot of people use MG stuff, but I steer away from it because I have never had anything good to say about it....MG fertilizes may be OK but their soils suck....
Well said AJ!!!