Feeding or light issues?

Hello everyone!

My plants started to show some yellowing and brown spots on their leafs.

These are 3 white widow autos from dutch passion.

First I thought it was something related to the nutrients I used (they were in bad condition). So I changed to a new and more reliable brand and bought an EC meter. (Last feeding 1.5 EC)

The problem still persists!

I water 2 times a week, once with nutrients once with plain tap water.
Ph: 6.5

The smallest plant is the least affected .... That makes me think it shouldn't be over fertilization.

What can it be?

Now I'm suspecting it can be light burn... But it doesn't really look like it.

I have some powerful Samsung leds.

Could it be it?

Plant 1: worst affected.
Image 1: before taking some top leaves

Image 2: after I took the 2 most affected top leaves (and better quality image)

Image 3: the leafs I took off the top.

Plant 2: affected too but not as bad as plant 1


Plant 3: smallest and least affected plant

Probably nute and maybe light burn. What medium are you in and how have you been putting fluids on them. They need a good flush every time you put fluids on them to wash the residues out of the rootzone. Have you been doing that? Plants look lime green so they're low N or it's locked up in the soil. PH of 6.5 shouldn't lock it up though; but if you haven't been washing them the rootzone is probably kinda toxic. If you have been washing them a lot then the dose is too low or you haven't been using the 1.5EC mix very long.
Not much time left from the pics since they're autos. Doubt you'll green them up either this late. Wash if you haven't been doing it and fert them right after so they don't go more deficient. My 2 cents anyway.

Overferting ---> Low pH and mineral excess ---> Nutrient lockout.

You probably started giving nutrients in already fully amended soil without the plants telling you to do so.

I typically only use water for the first 4 weeks after transplanting in amended soil. Let the plants tell you what to do.

from my first hand experience and i have had 2 grows go that way same symptoms at this point you Will have a harvest but your plants will slowly die you can try a flush or adding nitrogen i tried everything but once the leaves started dying that was it I still got 9 ounces of good smoke but the buds never really fattened up and by week 7 they were all but buds left no leaves at all

If lights are powerful, nutes co2 and everything goes up with higher dli. Maybe not feeding enough. Just a thought.