Help from the experts....

My girls are about 4.5 weeks into flower and I've noticed some of the leaves are yellowing and the leave are getting crispy. My thoughts are cal/mag?? I've learned a lot from you guys over the last year so hoping someone can help. Did a complete flush on Friday. Went back to normal feeding schedule today.
Here are the particulars that typically get asked:
400w hps
3gallon hempy pots all perilite
sensi bloom nnute
ph is good. Temp is 74. Exhaust fan as well as another fan blowing clean air into grow room.
Thanks for reading.

looks like nut burn,if yr temps are what u say that would be my geuss

yah Mag def. use the Cal/Mag every month as a preventative.

pellet lime ,or garden lime ,will also help to prevent that .

What do you mean PH good? Doesn't look good from the pics? Nitrogen looks lacking and definitely calcium. Magnesium will be next(are you seeing striping yet). Looks like nutrients have been locked out for awhile now. Perlite holds next to nothing so complete nutrients(balanced 5.6-5.9) is required every watering. Look into a 2 or 3 part nutrient line and these will cover most of your issues, generally cal/mag is the only additional bottle you might need.

Johnny-ph is 6.9
sensi nutrients are 2 part and ph balanced.
perilite does hold very little liquid. Which is the purpose of the hempy pots havering a 2" reservoir at the bottom for the root system to draw from.
Thx for the info