Seedlings are like private school kids; they are very sensitive and react to nearly everything. Those seedlings all look healthy to me.
What I would suggest is next time pot up in smaller pots (~5L) first before going into the final bigger pots, unless you are doing auto flowering plants then potting up directly into the final pot is the way.
Seeing as we are here in the bigger pots already, I would then also suggest to water lightly around the circumference of the plant instead of directly on top of where you planted. You don't want dry dry coco in your pot because it can be sometimes difficult to rehydrate, and you also want to promote the roots to work and seek out moisture around itself.
Don't worry about the pH up until now, if you keep watering at 6.5 you'll be alright.