I'm always very paranoid of light burn--it seems like sunburn in that it always seems to show up later instead of right away. If I drop water on on of my leaves and it burns the leaf the burn wont start showing up until the next day unless your light is sitting on your plants. I use 50-50 Cal Mag and nutes all the way through my grow and the one time I lowered the cal mag I noticed a deficiency within 24 hrs (green veins, yellow leaves) that disappeared with 24 hours after I readjusted the dose back to 50-50. Good luck...

PS It won't hurt your plant to raise the light and may very well help. Your ph is rising for a reason if you're already using distilled water. Have you been raising your light in line with the growing? I'm throwing everything out here...