I kinda think over watered and nute lockout. The red could be an indicator of lockout or female plant. The almost look nitrogen toxic, except the yellowish one. You might consider repotting to the next size up container. If the roots are thin and stringy, it is over watering for sure. If they are nice and white and fuzzy looking they are healthy and watering has been ok.

I would not be giving nutes at this stage at all, myself. You might also want to get a better way of checking the PH, you sound less than confident in your current method.

Acutally, they look pretty good so far.

EDIT: Regardless, looking back at the photos, those pots are too small, you need to get them into something about twice the size they are in now. At that size in those pots, it should be hard to over water them.