Leafs turning yellow from the inside out

Any idea why the back one is yellow and front one seems fine? I've given them nutes probably two times a week. At most three times a week. The last two feedings I've given them maxigrow, maxibloom and calimagic. One half teaspoon of grow and bloom each per gallon. 2.5 ml per gallon of calimagic. Thanks in advance!

You’re watering on a schedule it sounds like. Yellowing upper leaves can indicate overwatering.

What are you growing in? Are you feeding every time you water?

Three are THC Bomb and one is a bubblegum. The one showing no issues is the bubblegum one. All three THC Bombs are showing yellowing but that back one is the worst. They're in a mix of soil but they've been in veg for a very long time. They were germinated last October. And then I just didn't do much of anything with them until this month, as it's now legal in my state.

I give them about 4-5 gallons of fresh water a week. It is watered with a water pump on a schedule. And during each week I additionally feed with nutrients another 2 times or 2 more gallons.

I feel like maybe I over did the nutrients for this particular strain. Flushing now. And then I'll let them dry up to make sure they're not over watered.

Looks like iron deficiency, which mostly hits new growth. Most likely a lockout from some combination of, root issues, overwatering, pH or antagonism from other elements.