I grow in coco coir and I always make sure of my pH before I water...I don't even trust pH meters, I use GH pH indicator drops and go by color. Piss yellow is what you want Also, if that is coco you are growing in, never let it dry up. You can't let coco dry up as much as dirt.
I'm curious if your not watering enough at a time. They are wilting and nutrient starved. Try being a little more generous and let some water flow out the bottom.