The soil I'm using comes from my garden, where I got hit by planting various vegetables (that is why it is a sprouting plants).
I'm using this 1 liter pot to control the size (I've seen good results in a pot of butter).
Reading a bit, I saw that roots could be out of space. It could be lack of nitrogen, but the soil is not so poor and she has only 6 weeks. Also, at 7:00 AM I'm putting in outdoor and at 19:00 PM i put in 60W CFL (total 24/0).