No more yellow leaves spreading problem, it was the lack of nutrients for sure ! Thanks for those who helped me ! :)
Something to consider for my next grow: I decided to grow 10 plants to get a chance to have a decent harvest as it is my first time but it takes too much space, I barely have room to move myself inside the box and the plants have less light. I also think it is the reason it's too hot inside the box, when the plants were small and the outside temperatures the same as today, it was was less hot.
Next time, I'll grow like 5 or 6 but making them bushy as hell !!