On day 51 plants were:
- watered with a solution of NPK 4-6-8 + micronutrients + Bionova PH+
- put under warmer and more powerful light (2452lm 2700k)
I'm still struggling with the pH even if up to last week I always addded hydrated lime to the watering solution.
I switched to Bionova PH+ (potassium hydroxide) to achieve faster pH increase.