Bottom leaves yellowing early flowering. Nitrogen, Magnesium deficency or normal?

Cheers to everyone in this forum! I have been lurking around a long time and learned quite a lot from all the posts! Thank's to everyone contributing.

It is my first grow in years (did an indoor grow once) and it is going quite ok.

I am in the 1st/2nd week of flowering (I am growing outdoors on balcony) and some of the older lower fan leaves are getting yellow. No brown spots no crinkled leaves but getting just plain light yellow. I attached pictures where it doesn't look to bad, but this is how it starts. It ends with them being completely yellow and falling off.

I freaks me out as it is too early in flowering for my taste to get yellow leaves.

Steps taken:

I have watered with nitogen grow fertilizer to counter it and even foliar fed the leaves.

Further steps planned:

Next watering mix of grow and / bloom fertilizer (I don`t want to overdo the nitrogen) and foliar feed the fan leaves with grow fert.

Question:

How often should I foliar feed this leaves? It looks like nitrogen deficiency and not magnesium, right? What else could / should I do? Is the growing pot too small? (I wouldn`t like to put it in a bigger pot)

Infos:

Strain unknown (bought cuttling from store; it is legal in our country); Indica?!
Soil with perlite (25 l / 6.6 gallons)
Outdoor balcony
Started flowering 1/2 weeks ago; In bud stretching "phase" right now
Plagron grow fertilizer (European well known brand for growing MJ)
Watering every 3 days on average (more often during heat wave obviously)

Thank you for any help in advance! Cheers!!!

it is pready normal when the lower branches dont get enough light, if its only isolated to the very bottom, it shouldnt be a problem

bugs?-
.........

Thank's for the reply. No bugs/insects to be seen. Hope the fertilizer does do the trick.

looks good man....some nutes wont hurt. good luck

...more than likely, with such a dense plant, those lower leaves needs light, like conepuller mentioned.

dude amazing plant tell more about it............good luck!

most times if the plant is going yellow starting at the bottom and working it's way up it's a watering issue..too much/not enuf..you said you foilar feed between regular watering and that could be the issue..i've had it happen many times esp with clones...