i think my strawberry cough is sick. Please Help

Hey guys I'v been a medical patient for a few months now and finally desided to do an indoor grow. I'v done outdoor a few times without problems but i think I'v done something wrong. I'v got 13 plants currently going in veg. 11 from seed which are about 3 weeks old maybe more. The seeds took longer than normal to germinate about 5-7 days. One of my best a strawberry cough i think is sick. Its lower two leaves are turning a yellowish color and the upper leaves are cupping upward. plant is in a 7 gallon pot, soil is Foxfarm Ocean Forest, its under a 600wt HPS lamp(about 3-4feet from plants). room temp is kept between 76-78F. I have been feeding them Foxfarm's Grow big, Big Bloom, and Plant Success Soluble for Living soil & strong roots for the last week and a half. the last time i feed them was when i noticed the problem which has spread over half of the two leaves in the last 2-3 days. thinking it might be nutient burn or something from feeding them but not sure. planning to flush the plant in the next day or two. out of the 13 plants this is the only one doing this.sry photos suck they were taken with an iphone3

I know this is late but did you ever find out what the problem was? Did you check the ph levels and the ppm? I thought that yellowing of leaves meant that there is a nitrogen deficiency and you need to add more nutes, not less. I'm not sure though, I'm a noob.