As far as i can see from the pictures it is only one leaf?Chillax and smoke a bowl.If it is only one leaf it could have been caused by anything.If this is eating your whole plant up time to worry.
Ive had cold water drip off my ac on a plant and cause that little spot.If you shoot your bulbs and hoods with windex.BE CAREFUL.it will cause spots all over your leafs of outright kill them.If the rest of the plant looks healthy let it go.Nute burn will show up all over the plants leafs curling tips browning leafs.If pk over dose all kinds of weird things can happen.curling leaves..premature yellowing.To much N..dark green curling leaves.Burned to brown crisp if you really over do it.Most base nutes systems will run a plant just fine if you just read the direction on the bottles.To much humidity can screw your leafs up ..especially on the lower of the plant if you dont trim them out and let air flow through them.Mites will cause little white spots to start appearing on your plants leafs normally starting at the lowers and working their way up.You will in bad cases see spider webs developed on the plant.Leafs will start turning yellow from the critters sucking all the life and nitrogen out of the plant.On the under side of the leafs you will see what looks like sugar running around..those will be mites..
If that is the only leaf on the plant that looks like that..dont worry about it.Pull it off if it annoys you that much.
