NEED HELP Please... Bout To Start Flowering and I'm Starting To See This!! HELP

I have been giving em RO water, My pH 6.5-6.6 TDS 950-1000, In 3 gallon grow bags Using Black Gold Soil
Nothing but Advanced Nutrients Sensi Series..
Everytime i watered or fed, I always added Cal/Mag to my water.. Im wondering if that was too much, in which caused another problem...
I would really appreciate any help guys...and how to remedy this.. Because I want to start Flowering
And also... what is this that my plants are starting to have? Thanks

have you fed her at all? if so wat and how much, I would still go as planned but we need more info to help buddy

Yeah i feed once every week... Advanced Nutrients: Sensi Grow A/B

And I'm about to start flowering them with Advanced Nutrients: Sensi Bloom A/B

Im running them at about 950-1000 ppm
pH 6.5-6.6

heres what they Look like...
I Have: CHEMDAWG 04, GRANDDADDY PURP, SUPER LEMON HAZE, AMNESIA, HEADBAND707, SOUR DIESEL, PURP DIESEL

If feeding is on point and not the issue. Then maybe those leaves showing brown nectrotic edges/spots are lower canopy leaves. It looks like you have a thick canopy (looking good) but ive noticed when lower leaves begin to get cut off of light they begin to die very slowly. Thats what i have seen in my experience. The first pic looks like magnesium def. Notice the dark veins with light green in between. Im sure other people will chime in with ideas. Looks like your well in your way to a massive grow.

Yeah, Thanks...I've been doing it for some years now.. I have a schedule and all that, I keep my room very clean (Sterile Clean), I Watch my TDS & pH Levels Etc..
I never over fed, when they were little, i worked up to the TDS i'm at right now, They have never had Nutrient Burn, Root Rot, Etc...
I was wondering if its because everytime i watered or fed, i always added Cal/Mag to my water (Because I use RO Water)
and in me doing so caused a Magnesium Def.
If so... How do I REMEDY IT?