Plant #2 is sick I think

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.

To diagnose you need to check your runoff water for ph and ec levels. Adjust these according to your grow method. For veg your ph needs to be 6.2 to 6.5 ec should be around 1.8ec, 900 ppm to 2.0ec 1000 ppm. Cheers