@Mr. Grow It , my previous grows in coco I ran 6.3-6.7 and never had seedling issues. This grow I decided to try the common 5.5-5.9 and showing issue immediately. Started with 5.9 first water, two days later 5.5, two days later 5.7 and next day brown spots on fan leaves. Before I work back towards 6.3 like my gut is telling me me to can you think of anything else that may be an issue before I drop this low pH experiment? Hydro crunch coco (rinsed thoroughly and buffered with Cal/mag, 30% perilite, hps veg bulb set at 400 at 33 inches(had it lower bit the plants were trying to lean away from it. Now standing straight up), no nutes yet. I've never had an issue this early and the only thing I've done differently is the lower pH. These are the (photo) G13 pineapple Express which I've grown numorous times. (Side note I add calcium powder, epsom and diatomaceous earth to medium which I've also always done).