Do you think it's too much or too little fertilizer? I enriched my old soil with worm humus and premix, all from Biobizz. The humidity is consistently at 60%, and I currently have a PPFD of about 430. Since the 2nd week, I've been adding half of the recommended amount of Bio Grow from Biobizz.

Looks to me more like a slight nutrient burn combined with small pH fluctuations and not a deficiency. You mentioned that you reused old soil, but it was properly treated with Biobizz Worm Hummus and Pre-Mix. The Pre-Mix is extremely strong and actually meant to fully recharge soil for a complete run. On top of that, there are the nutrient-rich worm humus components, and since week 2, you've already been using Bio Grow, even if just at half dosage. For such young plants, that's quite a lot in the root area overall. The bright yellowing and slight twisting right at the new growth often indicate that the plant can't properly absorb micronutrients because the soil is either too "hot" or the pH is a bit outside the optimal range of about 6.2–6.5. This happens quickly with organic mixes. The climate and light, on the other hand, look absolutely fine with 60% RH and 430 PPFD, so I would rule out light stress. I would first completely pause the Bio Grow and only give pH-adjusted water, around 6.3–6.5. The soil needs some time to stabilize itself, and the plants need to grow into the strong soil mix. There's already more than enough food in there 😄 Happy Growing Growmie🌱