Check this out... http://boards.cannabis.com/grow-faqs...mping-off.html ...just a thought, however it appears that whatever it is, only the first set of fan leaves are affected...with only 2 fluorescents your temps should not be too high...

I have had similar looking problems before and they have always recovered, I would just keep an eye on them, don't water them till the soil dries out, keep an eye on the new growth, if it looks healthy you're good, (the affected leaves may get worse, and dry out).

Good luck!