Without pictures for confirmation, I thought it best to rely on the meager info. given in the original post to form an opinion. Since the poster mentioned that the "first leaves have a light
green pigment" it is very likely that these are embryonic leaves (cotyledons) and it is normal for these to wither and drop off. At 2 weeks old, It is highly unlikely that the plant is any-
where near mature enough to be showing any indication of a micro-nutrient deficiency such as Mg. My best "suggestment" would be to read as much information as possible contained
within the stickies of the newb section.