Details: happening on 1 of the 2 plants in this tent over the last 24 hours. Spots appear on 4 lower leaves. Plants are 21 days old in Fox Farms Happy Frog soil. Temp 75%, RH ~50%. Have only watered with pH 6.5 water, no additional nutrients. CalMag+ added at 4mL/G to the last 3 waterings. Last watering was 60 hours ago. Lighting is 1x Mars Hydro TS1000 running at full blast. I do have exhaust extraction and a carbon filter inline. I've deeply inspected for pests and haven't seen a trace of them. This plant is being mainline trained. Topped about a week ago, and tied down over the past 48hrs. Any ideas?