Żółte liście

The soil is new. I never use soil twice. Tomorrow I will water, I will add nutrients again and add calmag. A lot of purple stems so it's probably hungry.

The advanced nutrients is supposed to be effective regardless of PH. 5ml of cal mag to one gallon of water has helped a previous grow with yellowing coloration like that. I wonder if you have been reusing soil?

The pH with these nutrients was 6.3

So I water her with 1 liter every 4 days, the pot is 10 liters, so I definitely haven't overwatered her. Today I watered the plant and the runoff pH is 5.7. From the very beginning, I've only watered with water. I only gave nutrients that one time. The manufacturer says to give 4 ml, I gave 2 ml.

This could be a few things. Hard to say without more information. It could be over watering, it could be a ph in substrate issue, it could be not enough feed or too much. Going off the little information you left I think it is a ph issue in soil. I think you fed it strong plus dropped the ph causing it to bottom out. Based on the dark green I see on other leaves. What is the ph of the run off water. That is what you need to be watching closely. The plants generally like a higher ph when flowering the vegging. I believe you just did the opposite. .1 ph change is a big difference in roots.