Help Is this a Magnesium def if not wut?

Hi is this Magnesium def due to maybe to wrong ph? Its only on oldest bottom leaf's atm and only on 1 plant outta 3. I just switched in last 5 days from pure happy frog to happy frog + coco coir n coco chips. Id have to say I'm bout 50/50 hf/coco. I might be guilty of slightly over watering but i got just a lil bit of Epsom salt in mix and a lil diatomaceous earth been feeding with 4 little drops of super thrive, quart cap of fox farms grow big per gallon. I've also ran 1 feed so far with recharge at 1/2 tbs. I've got no pest my stick pads after 2 weeks have had even 1 gnat on them. I don't have a real ph meter atm i figured i could make it 2 months off the ph drops. I know it might not be the most accurate but figured it would be good enough. My only guess was slightly off ph or mag def but with epsom n my soil/coco mix i figured maybe ph then or even the fact they were n slightly less than 1gal pots so i repotted to 5gal fabrics, but nothing has changed and i can sorta see maybe 1 new leaf starting to turn from green to like the bottoms started. So figured id reach out to someone.

It's really hard to say at this point without an accurate pH reading you could have some type of nutrient lockout. If it's lockout from pH then adding more nutrients will only complicate things. If it were my plant I would get a pH meter make sure that's under control see if it corrects the problem and go from there

Nitrogen toxicity

Soil is too hot (too much N)

Were the leaves perfectly healthy when you just potted them? I can't tell if thats a seedling or clone.
Could be from a minor stress when they were initially potted and took time for everything to sync. Also hard to tell by the photo but your coco looks like it could be completely dry?
Never let it dry out as that causes ec buildup.

I'd go with Fatleg77's post, proper water PH is foundational to success.

Exactly, cause he crushed it with Nitrogen