Bottom leaves turning yellow

bottom leaves are turning yellow on edges on a few plants ..15 days old about 10 inches tall the bottom leaves are turning yellow on edges heres photo.....

ph is 6.5 plants seem to have been thriving this is the first sign of anything, as i said they are 15 days old

anybody? its my first grow so any help would be appreciated

Maybe lights to close? They dont even look close lol. Im baked sorry. One of these members will def. help you out soon