I chased it down for quite some time. I thought I had nute issues or PH issues. Turns out I DID have PH issues, but the low soil ph wasnt the cause, it only made the plant more susceptible to light damage. I was purposely trying to stay at the high end of the acceptable light range and shot myself in the foot. Too much light is hard to diagnose. The symptoms I look for are: 1) yellow tips on top leaves, 2)Veining on top leaves, 3) a lighter color on the top of the plant (bleaching...) and 4) other variables in control (ie PH, Nute level, moisture content, temp)