Possible calcium deficiency

after doing some research I figured it was calcium deficiency but I was not sure
So I took to the internet

Ffof soil
Fox farms nute trio
Week 4 of flower
400watt hps
(Sorry I hadn't turned them off)

Thats where i would look if all your other factors are in check. pH. Are you using RO water? Im about at the same stage of my grow as you and I notice my lower leaves looking shit sheeet... everything up top is fine. I got some slight burn from giving them full streght FF nutes along with full strength beastie bloomz.

apparently adding some cal/mag every watering wont hurt ya.

Too much fertilizer has made soil pH acidic and locked out Magnesium amongst other minerals that are now antagonizing eachother.

Or the plant just needs higher Mg dosage.

Are there any signs of problems on leaves up at the top of the plant, or only on lower large fan leaves? I cannot see close enough in the full plant pic to determine this.

(Make sure you're not overwatering; watering them too soon when they don't need it.)

Greetings.

Did you switch to bloom formula immediately @ flip?

Between watering, Do you dry them out: 25%, 50%, 75%+
before you water again?

How do you feed them?
Feed/feed/feed etc?
Feed/water/feed/water? Feed/water/water/feed?

Getting run-off from bottom and not sides?

FFOF pH range is 6.2-6.8, where are you?

Deficiencies are almost always calmag related when growing in soil and using common nute formulas.. By supplementing with calmag every watering you rule out that as a possibility.
This could be a lot of things. PH, buildup of salts, Looks like nute burn on the tip of leaf in your hand. Also looks more like N defficiency than cal mag.

The good news is that you are in week 4 and only have a few weeks to go. To be honest I've harvested nice buds off of plants that hardly had a fan leaf left

Personally, I gave up on trying to PH my nutes when growing in soil. Testing runoff didn't really seem to give me useable data. Most nutes geared towards MMJ have buffers in them to self adjust PH.

Get the calmag asap and try to answer the questions from CX... Also what PPM are you feeding them? If you don't have a PPM pen you really need one. They are super cheap. I generally feed at 900 ppm during flower (In Soil)

Also, what type of water are you using? If your tap water is high in PPM out of the tap then you will always un into issues. Since I bought a cheap RO filter things have gone much smoother. My tap water is 500 PPM out of the tap.

I use purified drinking water and feed every other watering with 1/2 strength fox farms nute trio(started bloom after switching to 12/12).
I use the GH PH drops and usually bring the ph to about 6.5 to 7
My runoff ph is usually the same(6.5-7) so I assumed it was not nute lockout. I Only water when the soil is completely dry an inch below surface.

As for my leaves up top I have only noticed a slight yellowing on the very tips( I will provide better pictures soon)

I apologize for any lack of info and thank you all for the help

(Edit)

This branch shows the yellowing at the tip of the leaves