What's this seedling problem?

This plant is representative of five plants started from seeds on 4/1/10. They've been growing in soil under T5 lights.
The problem seems to be confined to the lower leaves so far, but looks like it's working its way up the plant.
I think it's a nutrient problem, but I've never had a problem so early on with seedlings. I couldn't find a good photo match in the forums.

Thanks for any suggestions.

N-n-n-nuteburn! Flush and feed with plain water for a week. Start on weaker concentration of nutes next nute feeding.