Week three flowering - strange spots - can't identify.

Hey folks -

I am at week 3.5 of flowering and am starting to see a substantial number of brown spots. I initially thought I had a cal / mag eficiency so I acted accordingly - no love. She needs about 1 gallon of water every other day. I alternate just water with CALMAG and then water with CALMAG and the FF trio at about 1/2-3/4 strength. Note the browning of both tips AND in the leaves mid sections in the pics.

FFOF
3 gal Smartpot
FF big three trio
Runoff pH - 6.7~
Water going in is adjusted (GH) to around 6.4

I can't figure it out. This is my first grow and am terrified that something bad is happening when I am so close. Anyone able to help??

Looking like some nute burn to my novice eyes. If you are running in a hotter soil then perhaps go to quarter strength with the trio and see how she perks up. Also lower nitrogen during flower. Good luck!