MistaOCanswered grow question 25d ago If you’re consistently running into issues around day 15, that strongly suggests the beginning of a nutrient deficiency. This is especially common when growing in coco substrate. If you’re using coco, it’s important to start light feeding from day 1.
One of the most critical factors is the pH level of your irrigation water. Coco doesn’t buffer pH on its own, so you must maintain it at around 5.8 consistently.
As mentioned, early fertilization is key. If the lower leaves start yellowing first, it’s very likely a nitrogen deficiency at this stage of growth. Calcium and magnesium are also in demand and need to be added as well.
An EC value of 1 might actually be a bit too high for this phase, and that could be contributing to the issue.
Also, consider transplanting your plants into larger pots soon. If they’re around 15 days old now, this would likely be a good time to do it.