Does that soil have fertillizer already in it? That very well may be your problem, as the seedlings we started in soil that was too hot (too fertilized) for them, yellowed and stretched.

Oh yeah, after second look, it appears to be nute burn. Notice the browning tips of the leaves? Before 2 weeks its too early to be a deficiency, since the plants don't need food for at least two weeks. Try flushing the soil thoroughly next time you water, use 3-4 times the volume of the size of the pot.