Question about nutes in coco (again)

Alright.... I'm starting to get this coco thing down. They've been looking good for a while but I'm in week 2 of flower and now I'm getting yellowing on only the big fan leaves on the top of the plant, everywhere else looks nice and green. I doubt it's N def, because even though I switched from Bio Thrive as my extra boost to Humboldt Crystal Burst I'm still feeding them the same full strength Canna A and B coco nutes which should have all the N I need to flower.

Now the question of CaMg. I have been adding it in along with the Canna AB at half strength and just now I'm getting the yellowing in flower and I'm wondering if 850-900 PPM (total) isn't enough for them at this point, or if I'm actually giving them too much CaMg and creating lockouts. I watered them last with fresh pH'd water (which is always, nutes or not, at pH 5. but nothing really changed. I have to water again today so should I give them more? I usually feed with every watering, about every 3 days, and they don't seem to be drinking any more water than before

Here is the actual breakdown of nutes they get per watering
-15ml/gal of canna A
-15ml/gal of canna B
-5ml/gal of GH CaMg+
-10ml/gal of Cannazym
-2.5ml/gal of Humboldt Crystal Burst (its a 0-15-15 so I'm going light for now)

This all equates to a gallon per plant of 850-900 ppm (1.8EC is how I actually measure it) water at 5.8pH every 3 days. They are all the same size plants and in 3 gal pots with a 50/50 coco perlite mix

Yellowing only new growth is likely low phosphorous.

Small changes make big differences.

Also coco likes ph a little higher. What's your runoff ph?

show a pic of the full plant for the best answers. is your light too close? sometimes they get slightly bleached,

Whoops I had pics but the didn't upload sorry.

My light is about 15 inches above the tops of the plant. Its cooled and my temp sits at 75.

I was pH'ing to 6.2 before but I was having some problems, and a few veteran growers told me to keep it at 5.8 and it fixed everything

I forgot to elaborate on something: I they were growing pretty fast and looking great when I switched to flower, when I fed them the second time since switching the light (about 5 days ago) they looked this way the next morning after the feeding (and this problem is only happening on 3 of them) then I gave them fresh water for the last watering and tonight I will feed again. Since then, no other leaves have turned yellow at all. And the light has been he same distance away, I've been raising it little by little as they grow but I've maintained a 15 inch distance so I doubt its bleaching. I figured it was lockout because of too much CaMg built up since this occurred right after feeding them

I ph at 5.9 but runoff usually drifts up to 6.1. Plants healthy.

I had a super skunk start this about five weeks into veg. I bumped up my gh bloom one ml per gallon (5 to 6) and that strain was forever grateful (still growing that strain)