Hey I'm not experienced and definitely not the guy to help you directly, but I can help you indirectly by telling you these guys will need more information from you.
Be as detailed as possible, such as whats the ppm and ph of ur solution. Have you done anything else besides changing the light cycle? What's the temperatures in your area. What light are you using. What nutrients are you using. Etc...
In my newbie guess, which you should take for a grain of salt, I'd say it's over watered.