First grow! Super excited

Timelapse! I've meant to get a timelapse camera set up since I first started this grow. I am reasonably confident that future weeks will include full-week timelapses. For most of this week, my plant has seemed to have stopped growing. It got to a point where the leaves were becoming wilted, which prompted me to add nutrients. I was a bit skeptical regarding whether it was a good time to do this, or if I would be adding nutrients prematurely. All has seemed to have gone well with the nutrients, as the next day the leaves perked up substantially. Mid week, I changed the light schedule form 18/6 to 20/4 because I figured more light would enable better growth. Currently, I am puzzled as to why the leaves have developed some light and dark splotches. Could this be a result of light stress? EDIT (in response to my leaf spotting question): Thanks to those who have responded to my leaf spotting question! I have raised the light from 18.5in (I never measured it until now) to the recommended 24in. There is no chance of nutrient solution getting on the leafs to cause the spotting, but I did spray the tent with water + (dilute) hydrogen peroxide in an attempt to raise the humidity. Maybe this is the cause? I am currently battling the relative humidity. As someone mention, it is low! If i plug in my room-humidifier, the humidity will get way to high (80%+). I've placed an open container of tap water + hydrogen peroxide mix in the tent, but it doesn't appear to do much! I'd like to note here that I am using liquid indicator drops for my pH, so the pH is only my best measurement at the time of mixing solution. My pH may not be as low as I indicated this week! I think I'll throw in some tap water in lieu of cal-mag supplements,. I figure my city's hard water may be of benefit here!