I've experienced this before when my led was too close, but the uppermost leaves were affected. . I've got 6 plants all on the same feed and only this one is showing symptoms of not being happy. The affected leave are midway up the plant. The plants spend about 9.5 hrs a day outside if the weather is ok and only 2.5 hours under light normally. When the lights go out I keep the 6in exhaust fan going and another 6in fan blowing in a bottom 8in hole to the tent? Does anyone have an idea why it's happening?