Leafs curling down and almost yellow color seedlings

I dont think It's either overfeeding or ph issue like previous posters implied. Why? Soil buffers PH and the plants are very very young. Full PH lockout would be expected much later even in a small amount of soil. Although its very early for Biobizz grow yet, 1ml/l is far from enough to be able to deform a plant like that. Also It take up to a week to release It's full nutrient content. Underfeeding also pretty much not possible at this early stage of plant life. So my guess would be, they got a lot of Light- and/or heat stress or got overwatered. Can you give further info on that maybe?

Droopy leaves suggest there is no turgor. Yellowing so early, clearly you have been feeding grow nutrients so the chances of adding more fertilizer and expecting it to get better probably not going to help if it hasnt in 2 weeks. Something is messing with the cycle of water, if water can't leave the stomata through stomatal conductance then nutrient won't uptake. Plant looks like it can't perform gas exchange in order to pull water up along with nutrients. Alot of reasons thay can happen. I'd ask what your rh is but I'm sure some guide somewhere told you that seedlings love 75%rh. At close to 80% stomata close almost entirely. Lack of a better term to prevent drowning in the moist air. when relative humidity (RH) is high, there is effectively less "air" available in the same space. This is because high humidity means there is a higher concentration of water vapor (H₂O) in the air, which displaces other air molecules like co2 and oxygen. Seedling needs the scarce 0.04% co2 way more than it needs 80% water vapor taking all the real estate in a tent. While both photosynthesis and stomatal conductance are crucial for plant survival, they are driven by different mechanisms. Photosynthesis, the process of converting light energy into chemical energy, is primarily driven by light and CO2 availability. Stomatal conductance, which regulates water and CO2 exchange, is primarily influenced by factors like water status, temperature, and humidity both in medium and air.

Increase BioBizz Grow to 2–2.5ml/L for young plants in coco. Consider switching to a mineral-based coco nutrient (like Canna Coco or Advanced Nutrients Coco) — they’re more immediately available in soilless setups. Or add microbes/enzymes to help process BioBizz organics in coco. 2. pH Imbalance Coco needs water/nutrients at 5.8–6.0 pH for optimal uptake. If pH is above 6.3+, it can cause lockout, even if nutrients are present. Fix: Double-check your pH pen and solution. Stick to a target pH of 5.8–6.0 for coco. 3. Overwatering or poor drainage Coco needs to dry slightly between waterings, especially early on. Constant moisture + low oxygen can cause droop + yellowing. Fix: Ensure pots drain well. Let the top inch of coco dry out a bit before watering again