that's a good light, Try some Pro Mix HP or Sunshine #4 is also good for how we grow. I've been using PMHP and recently our store ran out so I tried the SS#4 and It seemed to work good also, But again I think you ran into the same thing I did when I forgot to move my light back after I put my seedling back under it and they did the same thing I see yours doing. stretching like that I just left the light where it was and waited a week longer for the new growth to appear, Good Luck Happy Grow !!