Unless this continues throughout the next two sets of leaves, I wouldn't worry about it, Cannabis plants can grow some odd and weird leaves at times, more so autos I have found. Your plant should be ok and keep growing normally. You would have to do something really, really drastic to kill the soil microbial life. 6.5 wouldn't bother them at all. Think 3 or 9 on the ph scale before any irreversible damage is done. Hope this helps.... Organoman.