Its normal for the bottom leaves to yellow on clones.. Plants use a lot of nitrogen to produce roots.. and when the plant has no roots.. it needs to take the nitrogen from somewhere else... such as the leaves :-) Once you flip your plants to 12/12 (which you may want to do fairly soon by the looks of things) wait a few days and then clip the bottom 5 or 6 branches off the plant... this will cause more buds to grow at the top where the light is.. instead of a bunch of shitty little buds on the bottom... I also agree that you should rotate your plants once in while.. especially if you have brighter and darker spots in your grow room... The little clone you were worried about doesnt look bad at all.. Sometimes they just take a little long to grow up... kind of like kids ;-) good luck!