Forma

Excess & deficiency in this case seems to be excess micronutrients & deficiency of macronutrients. A watering without nutrients & pH balanced to regulate PPM ➡️ then add balanced macronutrients in response to the plant's needs.

I'm watering every 3-4 days with 300-400ml. I think it's probably due to the temperature being too low in the grow area. Today I noticed it dropped to 15°C. Everything started when I switched from 24/0 to 20/4. It was consistently 25°C and now it drops to 15 in the grow area.

It is probably related to the soil being a bit too wet, or the night temperature being a bit too low in the box. Is it possible to put the grow box in a slightly warmer place? Try to place the cabinet on an elevation in connection with the heat, not too close to the ground. When the leaves are nicely upright again and growth is a bit faster, the new leaves will also take on a nice shape.

How often are they watered? The dirt looks bone dry with a cup tossed in.

Advanced Nutrients SENSI GROW part A / B pH Perfect

Are you feeding them at all? Does your soil have nutes in it? Really need info on the nutes, my friend... The answer is going to be there!