How they are?

The soil looks a bit coarse. There may be a lot of organic matter in it, which could be raising the pH or making it a bit too "hot" for young seedlings. I'd recommend doing a slurry test and checking the substrate's EC and pH. It's not 100% accurate, but it will give you a rough idea of whether the medium tends to raise or lower pH, or if it's overly active due to high EC levels. It could also simply be a matter of poor substrate saturation. From the photos, the medium looks quite dry to me. I definitely wouldn't add any fertilizers now.

for 21 days it's completely stunted unfortunately. Get a decent PH pen (eg: bluelabs) and go from there. Do you have proper but not constant airflow around the plants?

To me, it looks pretty good so far. The plant appears healthy, has a nice color. I'm not an expert myself and I'm still fairly new to growing, but from what I've learned, a PPFD of 300 (what i read in ur diary) might have been a bit high during the first few days after germination. That could possibly explain why it has stayed relatively small and very compact. As a rough guideline, these are the values I've noted down: Days 1-14 after germination (seedlings & clones): 150-250 µmol/m²/s From day 14 (early vegetative stage): around 300-400 µmol/m²/s If you're currently running about 300 PPFD and the light is hanging fairly close, I would try increasing the distance to around 35-40 cm (14-16 inches) and see how the plant responds. The very short internodal spacing does suggest that it's receiving quite a lot of light. That's generally better than having a stretched, leggy plant, but it can also result in very compact growth. Other than that, I'd stay relaxed for now. The plant looks healthy, and some genetics are naturally much more compact than others. Often the real growth spurt doesn't happen until the next few weeks. 👍 (Translated with ChatGPT, so if anything sounds a little off in English, blame the robot and not the grower.) 😄🌱

HI , As I can see, you have some yellowing on first leaves and later in the middle. it is posible you gave to plant to much light and now cal mag needed. also I would cut all leaves that stay en shadow. they are taking energy and do not give plant to grow as she have too😎 have a nice day

Possibly slgihtly too much light.. extreme levels are much easier to recognize the effects. A less than ideal environment would also result in slower growth. Possible it's a squat plant, too.. Definitely a bit small for 3 weeks above ground. So, you can probably improve 'something,' but may need to engage in a bit of trial and error to determine what the cause is for certain. If you did stunt them slightly with light, it can take some time to snap out of it. After it recovers, it may even want more light than was was given early on that caused it.. younger plants have different needs... the resulting node spacing of new growth helps guide you. Some plants are lanky, some are squat and there's no changing a leopard's spots in that regard. Your nodes aren't stacked directly on top of each other, so if it was the light, it was too much by a small amount and requires a small adjustment. if you get some weak lanky growth after adjusting the light, it's probably just a smaller-stature plant. Small plants in a large pot makes watering difficult to do properly. soil looks extra chunky which isn't best for the roots... could still improve other things that may improve growth rate in future. Even when you do things in a consistenly good way, genetic diversity is still a significant factor.

Looks quite good. A bit short and compact, light might be a bit too close. Give it some roots enhancers to build a strong root system if you want to increase the growth rate.