There's a chance that it's a nutrient deficiency however if everything in your grow conditions are accurate chances are you're over-watering. 3.75 litres to four litres is about 20% runoff of your pot size, and at this stage of the plants growth it shouldn't need that more than once a week, twice at most if it's dried out. Hopeful that this will bounce back and you'll have a healthy girl very soon. Following and sending well wishes your way ๐๐พ๐๐พ
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