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Your plants are showing typical signs of a nutrient uptake problem and not just a deficiency. The yellow new leaves indicate that micronutrients like iron, magnesium, and calcium are not being absorbed properly. The red stems and leaf veins additionally suggest stress or a magnesium or phosphorus deficiency. The most common cause of this is an incorrect pH level or uneven watering, especially in large pots. If you only water small amounts, the substrate won't be evenly moistened. This creates dry and wet zones, which disrupt nutrient uptake. It's important to monitor the pH level and keep it in the right range. In soil, that’s about 6.2 to 6.5, and in coco, between 5.7 and 5.9. Additionally, you should use CalMag, especially if you’re using soft or reverse osmosis water, to create a stable base. When watering, you should not only give small amounts but thoroughly moisten the pot until there’s slight drainage. After that, wait until the pot feels significantly lighter before watering again. This ensures that the roots can work evenly. If you adjust this, the new growth should become healthier and greener within a few days, even if the red stems may still remain initially.

Phosphorous issues.

It appears to me that this could be too strong light intensity causing magnesium deficiency. Light leaves on the top with interveinal chlorosis leans toward magnesium. Bottom half further from the light looks ok. Red stems and leaf veins happen with high intensity led lights. Like a sun tan to them to help protect themselves. If lower stems are normal, i suspect the light. I would recommend adding a cal mag supplement and backing the light off a couple inches. Give it a week or so and see if conditions improve. At very least should not continue to get worse or there are other contributing factors. Just my thoughts, Best of luck! Happy Growing!

Hi Grower! Suboptimal pH level (nutrient blockage): This is the most likely cause. If the pH level of your water/soil is off (ideally 6.2–6.5 for soil), the plants can't absorb nutrients, leading to discoloration. Calcium-magnesium deficiency: Red stems are a typical symptom of a Cal-Mag deficiency, which often occurs in the strain GG#4. Iron deficiency: Yellowing of the young leaves at the tip may indicate an iron deficiency, often caused by a too high pH level. Too much water (seedling stage): Although you mention that the top half is dry, 2–3 liters of water every 3 days in a 10–15-liter pot for young plants may be too much, as it hinders nutrient uptake.

Greetings, it looks a bit like they are getting too strong lighting. Red stems are an indicator of that. I can only say how I would personally proceed or what I would try. I would give the ladies a bit more CalMag, plus a bit more nitrogen. And furthermore, control the light intensity and maybe dial it down a bit. Otherwise, just keep observing and loving them. It'll be fine.😉✌️