The purple stem of the leaf indicates a slight phosphorus deficiency!
The deficiency could have occurred due to:
1. Incorrect substrate pH.
2. Too little bloom additive.
3. Too much nitrogen (grow additive).
Solution:
1. Set the soil pH to 6.3pH
2. Reduce the grow additive to 0.4ml/l
3. Increase the bloom additive to 2-2.5ml/l
✋😇👌 Good luck, bro!