stain on the leaf

A bronze spot and a little tip burn can be caused by quite a few things. Lighting, pH issues that cause lockouts of essential elements, heat stress including temperature differential swings between lights on and lights off, etc. Here my instinct tells me you've got a minor Calcium uptake issue. If you know you have sufficient Ca in your pot, you can check your pH (both the pot and your fertigation or water pH depending on what you're using). Although it's more likely to be an uptake issue centered on pH, you might also not have enough of that element going in -- OR have too much of another element or elements that are preventing normal uptake of Calcium. Take your time, look at it closely, and try not to act in haste. Try to think it through slowly then act when you're confident you know where the deficiency stems from.

Not septoria...........most likely slight burning from moisture on the leaf, 18/6 is best, 23/1 is not enough "sleep" time for a properly functioning plant metabolism.. 7-11-27 is not very good fertilizer for cannabis in early veg stage.