yellow grow tip

hello everybody i have been researching problems through RIU for about two weeks, and am not positive what is wrong. I started this plant about a month ago growing in miracle grow seed starter soil. I have never grown in soil before and thought that it would be less involved. I know that i am not over watering, and the PH is about 6.8. I had a problem with heat stress and burned the forth set of leaves. ever since the leaves have grown yellow curling down. Some new leaves are splitting down the viens. The yellowing is inbetween viens and seems to lesson as the leaves get older. it looked like a zink problem so i replanted into a larger pot and flushed the soil. I just dont understand how such a young plant can be getting nutrient deprived so early on. it has been in the 12 inch pot for about five days. any help is much appretiated.

The fact that you're using soil that already has nutrients in it makes me think it might have a little bit of nutrient overdose rather than deprivation. If you burned those top leaves odds are good they're going to yellow and die anyway. Are you saying the yellow has spread to the new leaves? Throw a picture up here and let everyone see what they see!

If the yellow is in the veins, it could be a phosphorus dif. it can happen in the veg state... are any leaves turning a greyish color at the end? are any stems changing a purplish color or anything?