What is the browning on the leaves?

I understand that you've probably just found this site because you're looking for answers and worried about your lovely plant, but without the correct information the community cannot and will not help you. I will try.... 1st of all take pictures with the grow lights off and fill in your nutrients and correct stain and breeder so people who have grown this strain can compare. 2nd. Going by the info you've provided I see a few problems and don't worry we've almost all been there. 3. If your led is 1000w that is alot of light. Even for a Big space with a few plants. Having it 20cm is far, far too close! 4. Ph levels should stay between 6 and 6.5 ideally, it does make alot of difference for correct nutrients absorbtion. Once a week or two you must water without any nutrients to move any dorment nutes around. 5.we don't know what you're feeding schedule is either but I would say you are or were over feeding especially in nitrogen. 6.watering with 3.5 l of water per day is a huge amount, half of that should be ample or even less! 7. Temps are to low, that could also be stressing the plant out. Sorry if it sounds harsh but if all your data is correct then there are a few things to correct on. Happy growing 🌱😊

just sseing a small part of your plant , and having no clue what you are feeding, if the other datas are correct... is a guessing game here. I see a number of issues, that are not as easy to solve. and in that state of grow arent solveable. growing is alot of learning. And i just want to say to you go and fill in your next grow all datas, write every acion down that you make on your plant ( watering, feeding, your nutrients etc........) only tht way we can look what is going wrong.. and you only can learn to avoid the same mistakes if you documet them.....hemp is very resiliant , you wont win a beauty contest with the plant, but she will survive and give you a harvest...... Happy growing

Looks like your grow light is to close. With cannabis plants that have light burn, your leaves can sometimes become yellow or red/purple, possibly with brown spotting, often with burnt tips/edges and margins that stay green. Leaves may also appear generally burnt in places when there’s too much light, especially when combined with heat or nutrient problems. Just back your light up two inches and watch things closely.