What's wrong with my plant?

your irrigations habits look suspect. 1) fully saturate.. no half assing it. If soilless, also get 10% runoff, religiously. 2) wait for appropriate dryback (or loss of weight or depth of dryness on top) and repeat. you look to be drizzling a little water near the base of the plant because that's the only spot that shows moisture. PRobably got a bunch of dry pockets and more moisture up top training superficial roots etc etc.. all sorts of bad things develop over time when you have poor watering habits. if the soil is as yan402 explains, treat it like soilless, in my opinion. Buy soilless/hydro nutes. Your house also won't smell like shit that way too. Full diet every irrigation with 10% runoff, which will prevent buildup of nutrients in medium.. At that point any symptoms seen are a result of the formula, which makes diagnosis easier, too.

Bro, your soil’s out of juice. Plagron LightMix only feeds for a couple of weeks, and 1 ml/L Fish-Mix can’t keep up anymore. At week 5 + pre-flower you need a balanced NPK + CalMag + micros source — or start feeding at least 2-3 ml/L Fish-Mix + a bloom or micro supplement. Leaves show classic N and Mg deficiency, not overwatering.