Where did I go wrong? Expected something, but struggling to pin this one down.

A light green or yellow coloring will begin to show on the veins and edges of the lower & older leaves – this is one of the classic signs of cannabis magnesium deficiency. You may also see red stems. Yellowing starts from tips from outside working in, Interveinal chlorosis is distinctive of magnesium deficiency but, although seems to be more going on here. First off your diary is partial, what kind of medium are you growing in? Coco substrates have a few unique chemical properties that can cause problems if not treated. Chief among these is the high amount of potassium naturally found in coco. This potassium tends to swap places with calcium in nutrient solutions, resulting in too much potassium and not enough calcium in your system. Fortunately, treating with Calmag is a good way to remediate this. In week 2 you mentioned nutrients then it went pear-shaped, what nutrients? Have you checked PH? is it within optimal range? Coir(especially chunks) as a soil is notorious for sucking out all the Cal and Mag if not pre-buffered correctly. All-in-one fertilizers either come with Cal-mag or no Cal-mag. Why? Alkaline water 7+ normally has enough Cal-mag floating around, calcium is one of those bitchy nutrients that screw up the uptake of other nutrients when in excess. This leaves the choice up to the grower. Guessing you got one without Cal-mag. Calcium is immobile, and Magnesium is somewhat mobile in that it can be mobilized but at a cost, the magnesium is being stripped from old growth and sent to new growth, the atomic structure of chlorophyll is lots of nitrogen surrounded by a magnesium core. Nitrogen lost its core, goes dark. The fastest way to remedy this is foliar application. Magnesium sulfate + Calcium Nitrate or buy fertilizer and add to the soil as per instruction. Good luck.

The plants do look like they're slightly. Overfed. What kind of bucket are you growing in? If they are cloth I would recommend taking a 5 gallon bucket filling it with water, pushing it down in there and letting it soak for about 10 minutes then draining it completely. Whatever you been doing for nutrients I would cut it in half in water about a third less than you have been. I think you'll be just fine

https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg

Easy what you did wrong. You took advice from people on this site.

Looks like an issue with potassium. either it is locked out or it is not given at a highe enough concentration. High P can cause some similar symptoms, too. I'd lean toward an issue with K, but use more information to eliminate possibilities. if you are in soilless/hydro context i'd recommend 180-200 ppm of K. If you are significantyl lower than that, it makes the decisions easy. A soil context is too complicated to just give a target ppm of your fertilization. it depends on what exists in the soil + your ferts. So, there is an unknown factor. Depending on the soil, it may be depleted by now or not or anywhere between. Trial and error ... familiarity with the soil helps.