Flush system. Clean with Dilute H202, Flush again. Check PPM of water. Add CalMag to bring base water to 250 PPM. 1/4 strength nutes adjusted to 5.5-5.8 ph. 85F is the upper limit for temp. At that age I keep PPM's of nutes around 350-400 (total). Def lower the ph. I grow in pure COCO, Modified hydro but it is so close to true hydro that the PH will apply to your grow too. Read what others are doing in the indoor grow section and search hydro/PH. Seems like leaves dont repair themselves from burn spots so watch new growth. Each grow is different as is each strain so make slow changes and adjust as needed. Good luck.