One yellow leaf often means nothing. Plants shed old leaves. But, I suspect you will start getting more and more yellow leaves, because you do not have nearly enough light. Those fluorescent lights I assume are feet away, instead of a few inches away from the plant. Even if they were inches from the plant they are not full spectrum lights. They were built for you to work, not for a plant to live. Buy a small desktop LED or Compact Florescent Grow Light. The LED are very inexpensive. Here is a link to one of the many LED Grow light that will fit on desktops. You want to make sure it has white or yellow light, not the purple light. Cannabis growers were told that all they needed were Red and Blue lights (When you have blue and red lights shining they make purple light or I and many call them 'Blurple'), so the market got flooded with 'Blurple' lights. They are much cheaper for the Chinese manufacturers to make. The latest data is showing this was incorrect. A plant needs a full spectrum of light, which should look White or Yellow to your eye.
https://www.amazon.ca/HIGROW-G...
