does anyone know whats wrong?

she has been in flowering for like 4 weeks in my closet grow box. it has i few brown dead spots on a couple leaves its not bad but it seems to be getting worse. i did see a white dot but i think it might have been from the old grow box that had white paint. and i seen a gnat flyin around but any idea what i can do to fix?

looks like nute burn mate try flushing next feed the cuttin down on nutes by a ml or 2

im not really using much of anything, i water with just regular water most of the time. i water with miracle gro liquid houseplant food maybe twice a week so maybe thats it.