Please Help Find My Problem! Pics!

Hey guys one of the newest leafs towards the top has a dead at the tip and yellow and brown around it, kinda looks like nute burn but since I dont use nutes so any ideas on what this is before becomes a problem. There is a couple of higher up leaves but they dont have any problems, so I dont think its heat stress. No other leaf has any signs of this either so I just stumped on what this is! So any ideas or answers would be gladly appreciated!

could be nutes that are already in your soil OR your soil is lacking nitrogen.

Well this morning I started to notice another leaf with the same problem so now im starting to worry. Im using some gardeners gold organic soil. Its really similar to Foxfarm organic but this has rooting microbes, which I dont even know what the difference is, but I guess better? Could that be a sign of heat sress? Because this plant is growing very rapidly so mabye its getting to close to light, Im using a 400w MH at the moment, and the plants are about 16in away. But im baffeled, im going to try my best to get another picture of this on here. So please help if you can!

thats a lot of foliage for not using nutes but honestly it looks fine, prune the leaf if its bothering you but I wouldnt change anything just because of that. wait to see if its starting to yellow from bottom then I would suspect not enough nute but for now I would wait

whats your water source btw?

Just tap water, then I Ph to 6.5, Ive grown using this water before but never have used the soil im using at the moment. At first I thought was now big deal, but now a lot of new leaves have dead tips on them, so I think there really is a error in my growing technuquie