My 2week old seedlings bottom leaves are starting to yellow i have 2 in 50/50 ffof and fflw and one 100% ffof the ones that have 50/50 are yellowing not the other i have them all under a 4 bulb 2foot 24w t5 light temp is 77* any suggestions what may be causing this would be a great help http://s162.photobucket.com/user/darthspankor1982/media/02926E9D-6A85-4956-8221-84AC432661FA_zps8q0rfpe8.jpg.html" target="_blank"></a>