I had the same look to my leaves and researched it. Came up with leaf rust which led to my spraying under my green light with
Rosenthal's Herbicide. Problem went away. That was my experience. Good luck.
bridge4 Reviewed by bridge4 on . Hydro - brown spots and dry leaves White Widow x Big Bud seeds Indoor growing tent 48"x24"x60" Hydroponic Rockwool surrounded by hydrotron Hydro bubbler system, 8 gallon tote with 5 gallons of water, leaving about an inch of exposed roots from bottom of 3" pots Tap water source Source water pH - 6.9 (treated down to 6.2, I just dropped to 5.6 tonight) Source water EC - 110ppm (I don't have a EC meter) 5 weeks old Using complete FoxFarms system and schedule Rating: 5