too much light ? or pot size is too small ?

Thats not because of small pot size (its not that small at all), neither light issue. Older leaves naturally dries, especially while they have lack of light, which is totally normal while they are covered. Not sure if other leaves got healthy color, due to photos under working light.. Can u make some closer pictures? Maybe from above, without lights. Saw u are using bio grow 1ml/l and I think its just too low dosage. Once she entered early flowering, she got slightly more needs of P and K. So, I believe she is hungry for nutri's. I would recommend use bigger dose of bio-grow and bloom (unless u just used bloom fert, then not). Bless