I am growing hydro and my girls are in their 6th week of flowering and I keep having issues with my leaves developing brown spots on them. It's not in same area association all the time. I have flushed my system. 2 x's, and I monitor my ppm and ph daily. I keep Ph between 5.5 and 6.0, and have lowered my nutrients to 750 ppm. I had thought it was nutrient burn or possibly a calcium deficienicy, so I have added cal-mag, and have backed off of nutrients. The girls are still doing great and getting nice buds, but I am concerned. I have attached pics. Any help would be great!