Yellowing middle and mainly bottom, been in this pot for 3.5 weeks

looks like start of n-deficiency. Paling that starts lower on the plant and moves up -- also tip-in progression on individual leaves -- is highly likely Nitrogen deficiency. If the rest of the plant is healthy and no other unique symptoms, try to increase portion of N without impacting others stuff as best possible. Side note: don't use that type of logic -- 'all the other plants are fine and were treated the same' -- doesn't fucking matter. Cause and effect matters. And right now you have an effect that is not a figment of your imagination. That type of reasoning will only lead to denial, delaying reaction and inevitably more problems over time. observe and react. So what if you treated all the same? Then, clearly the 'same' is not good for this specific plant. It is possible to have a formula (soilless/hydro) or soil recipe+fertilizer regimen that can work with 99% of plants, but that doesn't mean any formula can do it. Some plants are more robust to varying levels of nutrients than others... Take notes, make adjustments, and eventually 'doing the same for all plants' will actually result in all of them being healthy plants. Proof is in the pudding, not some inductive, top-down approach. a 1:1:1 ratio will not properly feed a plant by itself. you also have this in a soil, correct? And, that soil provides some pre-amended nutrients, too. So, it's difficult to confidently diagnose but this particular symptom is pretty straightforward compared to others that can be caused by multiple things. Leaf symptoms are more often indiscrete, meaning you need to cross-reference other things to eliminate possibiities -- mobile vs immobile, for example, will impact where the symptoms start on the plant. Whether it is paling tip-in or from petiole out is another. chlorosis and interveinal chlorosis are 2 different things etc etc... Even so you will run into situations where it could easily be 1 of several things causing what you see.