start of week 3

Nitrogen deficiency, possibly magnesium too (because of the obvious veins).

Sorry when you said made your own medium I instantly thought soil.. In coco.. Yeah there hungry.

promix bx comes with a 1EC charge, or thereabouts. This is plenty for a seedling for a week or tw, but not enough to feed a plant long-term. You need to be providing 100% of nutrition each fertigation in a soilless context, which this is. I use BX and HP all the time. Best to mix with some additional vermiculite or perlite, but that isn't the cause of what we see here. Probably low K. That's the element of promix's initial charge that is a bit on the low side of what you'll likely provide to the plant, so it's the first to be used up. 120-130 N 40-60 P 180+ K 100+ Ca 80ish Mg 100ish S This is what i'd suggest you target with some 100% plant available and 100% soluble fertilizers. This is a low starting concentration, too. 1.2-1.3 EC is a safe starting point. You can adjust as needed based on the plants in front of you. Local variables make exactly what you need different from other gardens more times than not, but it will be very similar in this particular regard. 1) always irrigate with a full dose of fertilizer and get 10% runoff or more, religiously. 2) wait for appropriate dryback and repeat. The 10% runoff is essential for soilless growing. This runoff water can be used on plants rooted in the earth, but should not be used on any potted plants. Or, throw it down the drain. Don't let it sit in its own piss. I'd suggest finding something similar to "Jacks 3-2-1" hydro Part A. These setups are easy to discern. a "Base" part that should contain trace elements, too, calcium nitrate and magnesium sulfate round out the 3-part fertilizer. The last 2 can be generic products of any brand. Masterblend, cropsalt, kosher-something, megacrop, souther AG.. and more have a similar 'hydro' setup. Not all of them put the trace elements into the "Part A" ... those brands should be avoided as they are trying to force you to buy the more expensive, branded version of calcium nitrate (or less likely magnesium sulfate portion). Even promix uses a ratio very similar to Jacks 3-2-1, except for the lower K levels i mentioned, it's essentally the same mix and that's no coincidence. These companies all based their products on the same knowledge base instead of trying to re-invent the wheel ... and then it comes out square or oblong, lol. Soilless method is one of the easiest to hit the ground running with a good formula, which Jacks and others provide. It should not be a struggle. Fertilizing and keeping a plant happy should be one of the easiest things you do.

She just looks hungry. Or your ph could be off in the soil. Around week 3 your plant is needing food. I would start feeding her a well balanced npk cal mag

Überdüngung. Gib ihr erstmal nur noch klares Wasser... und nen größeren Topf. 👽

What have you made it with. The only thing you can do is give water only. It's hot that soil

Synthetic delivery, you feed the plant final form no nonsense nutrients. No breakdown required. Organic delivery, you feed both soil and plant. But it comes at the cost of While plants can absorb both ammonium and nitrate, the majority of applied nitrogen fertilizers (like urea and ammonium-based products) are converted into nitrate by soil microorganisms through a process called nitrification. Where microbes break down organic matter into ammonium (ammonification), and then different bacteria convert ammonium to nitrite and finally nitrate through nitrification, making it plant-available nitrogen (N) for uptake, though plants also use ammonium directly Plants can readily absorb and use ammonium NH4+as a direct source of nitrogen. However, high concentrations, generally anything exceeding 20% of total nitrogen supply, can lead to problems. Understanding these differences is vital for using organic nitrogen and maintaining a basic understanding of what's going on under the hood. Gluck

Looks like something is affecting the big 3 cations, symptoms look like a mush mash of what I'd expect from iron deficiency (Fe) or sometimes magnesium (Mg) causes classic interveinal chlorosis (yellow between green veins), often on new growth. Maybe a symptom of early K. I'd be leaning more to a lockout. Nitrogen in its nh4+ form can antagonize Ca,MG and K. Impossible to be accurate without more info. Unless you have been bombing her with calmag or K I'd be looking at possibly N causing lockout of big 3. Nh4+ is generally found in much higher quantities when using organic delivery methods. Maintaining a stable pH is crucial for the nitrification of nh4+ . If pH is off even a bit the micros will just continue to breakdown and ccumulate nh4+ in a medium which will contribute more and more over time to a skewed ph. Rate of nitrtrification of nitrogen iirc is 3x4x the rate at a Ph of 7, as opposed to a ph of 6. In a perfect world you wanna hold 6.4 to 6.6 to unlock hydrogen but soon as she drifts to 6.2 or lower the breakdown of nh4+ into no3- will almost cease entirely. Ammoniacal nh4+ will take around 4 or 5 times more water to separate from soil particles. What you do is up to you. Gluck.