taches à 2 semaines de croissance

I'm going to guess this is your Cheese XL grow... (next time you have a question, there's a place to ask it right below your diary - this links the question to the diary so we know which grow you're talking about!). I think you're facing a calcium deficiency here - and it has a lot to do with the PH which is too high. You need to get this down to 6.0-6.3 for optimal calcium absorption... whenever you give it water or nutes, make sure it's ph balance between those numbers and you should be fine. You've caught the problem early and I don't think you'll have any trouble. The damaged leaves, btw, will NOT get better so don't expect to see improvement in them - but the newer growth should show these signs if you get a handle on your PH. Good luck!