Hey Elfie , damn , last time I was here you were using a incandescent bulb , now you're using a 600 watt hps
Wow !! Nice move ....
Your plants look pretty good considering it's a first or second ? Grow
I'd be proud of that one , she looks heavily sativa influence , and I've found the satvas tend to yellow up a bit more in finishing stages of flower , I wouldn't worry about anything , just keep doing what you are doing ....
One suggestion , you should definitely get an air cooled hood , and an inline fan to suck air thru it , that box is way too small for a 600 hps and it must be hot as fuck , also can be a reason why your plant can be stressing , that fan is just tourturing you plant by circulating hot air in that space ....
I see it's a closet grow , but that light is made for a much larger footprint , so either get a room or a box that's larger or definitely air cool that bulb , won't cost much ......