First signs of heat stress?
I've got two seedlings growing in my seedling box, a gutted pc case with 2 6500k cfls in it and a pc fan running for ventilation. The taller of the two is starting to show yellowing around the edges of the leaves and 1 of them is slightly curling up the others seem fine. The shorter of the two plants doesn't exhibit any yellowing on it at all. I doubt its nute burn as the seedlings are in a mixture of humus and manure with perlite added in in about a 2 to 1 manure to perlite ratio. The manure and perlite both have like .7 or some other fraction of a number of all the vital plant nutes added but I don't think that would be anywhere near enough to cause burn. Heres the single picture I managed to snap off before my cameras batteries died. They're charging as I type this so I should be able to get a picture or two more tomorrow.
You can always look back, but you can never change the past.