Underfeeding or something else?

i tried to look up contents of the fertilizer you are using and the data sheet is garbage.. no npk values nothing.. it's sugar and ferrtilizer is what i garnered. there's no information to go by. so all you can get is a guess. It also looks like excessively cramped space, so the vpd is probably low which means you'd need a higher concentration of fertilizer than typically instructed to mitigate that.. or don't brow it in a tiny space. that ring of weak light isn't going to do much for you anyway. looks like you have more than 1 issue concurrently. is this coco (soilless)? soil? Seems a lot of questions invovled less-than-healthy plants and bio bizz products, lol. I'm just gonna say it's some poorly thought out ratio and clearly isn't all you need. find a more complete diet. go soilless. it's easier.

Over fed, not under fed. Black blotches are from excess humidity, not a cal/mag problem. If growing in soil, 3 feedings a week is way too much........twice in 10 days would be better, with plain water between the feedings.

biobizz is soilless right? just coco? if so that all applies.. not to soil grows, though.

bio bizz instructions must be useless, lol. see a lot of questions invovling them and messed up canopies. i'd second the 'overfed' vote, too. Might even be locking something out, because there's more than 1 type of symptom going on. Check pH too.. but need to see how this progressed and make a more informed decision. When it's a smorgasborg of symptoms, reading leaf symptoms is even futher from discrete than normal. Balance could be off with some stuff too high and too low, too. soilless is easy peasy. a ratio and concentration of nutes that will work well and require minimal adjustments: N 120-130 P 50-60 K 180-190 Ca 100+ (depends on tap water a bit) Mg 75ish (depends on tap water) S 100-110 This is a light concentration that is safe to start with. A free phone app can take the percents from guaranteed labels on fertilizers and convert to ppm. there are internet calculators that cna do that for you too, so no heavy lifting needed. If deviating greatly from these numbers, good chance that is where the problem lies. In flower, you may want N ppm near 110 or so. A little lower, but nothing too drastic. 6.0 ph +/- 0.2 is fine.. hell even 6.5 can work. You'll probably get measurably more production with slightly more acidic than 6.5, but it is not something you can see with your eye as far as scale of that effect.

deine pflanze sieht für mich überdüngt aus