The yellowing on your plant looks to me to be either a nutrient deficiency or possibly nutrient lockout from too much of something. A little bit of fade at the end is not a big deal in my opinion but that is too much fade and too early. Also, the way that your plant is yellowing is not "normal", usually, when I see fade in plants it is toward the end of their lives, is confined to mostly the bottom of the plant, and is predominantly confined to the oldest fan leaves.
The answer to yellowing is not always to add more, sometimes it is the result of an imbalance causing a lockout of certain nutrients. Of course, the best way to know for sure would be to do a SAP analysis, but they are expensive and take time. It wouldn't be worth it cost wise for one plant, and with the turnaround time I don't think you would have adequate time to correct the issue once you got the results. If you haven't been heavy handed with your nutrients then lockout is unlikely and in that case, a good broad spectrum fertilizer could help.
To be fair I don't know shit about hydro, I grow outdoor in the soil, so take my advice with a grain of salt, good luck.
