6.5 is ideal range for mineral uptake in soil,i guess you running soil,isnt any information here,if in soil your ph of the soil is way out of whack,6.5 soil ph 6.5 nute intake
Looks like phosphorus (P) deficiency. Give them a good flush with bone meal. Our ladies have have a hard time absorbing P. Bone meal will help with your issues. Give em a good flush then let them dry out. Mix in a fertilizer that contains P. You might drop your ph a bit to 5.8-6.0.