personally speaking, I don't really think its the soil its self.. that's causing this problem.
If your feeding nutes to this young sprout.. that's where your creating the problem. Why? Well, its simple really. Most MG soils already have nutrients premixed into the soil.. enough for a good months worth of feeding. So, by you adding nutes, to a plant that's already getting enough nutes from the soil alone.. your over feeding the plant.
Now, I'm not accusing you of anything here.. (i've come across some "touchy" ppl on this site) so I wanna clear that up before hand. I'm not accusing you of nothing. But, if you are feeding the plant nutrients.. with the nutrients its already getting from the premix soil your using.. then yes, you are over feeding it.
If this is the case, then I would immediately stop feeding the plant nutrients.. as your not really suppose to start feeding a plant any nutes until its mature enough to handle the nutes. Which, usually, won't be for a good two to three weeks, of veg. cycle. But after that, you can start feeding the plant. But make sure that, if your using a premix soil, that is already filled with nutrients.. make sure that the soil is no longer able to "feed" the plant nutrients.. before you start feeding the plant an outside source of nutrients (the nutrients you feed it).
Hope this helped and best of luck to you.
peace.