what would cause this?

Idk but its on just one leave wanna catch it before it gets worse, im leaning towards nute burn??

Its either where leaves have been resting on it, calcium deficiency or potassium toxicity.

If that leaf's off newer-to-middle growth, its definitely calcium.

Buy some calmag and bobs ya uncle.

that looks like it's been burnt by a cfl

stringer420 said:

Idk but its on just one leave wanna catch it before it gets worse, im leaning towards nute burn??

Click to expand...

don't worry man the first 2 leaflets are from a light burn cfl grower? the tip of the 4 th leaflet is from nute splash burn apart from that your leaves are very good ie the plant is systemically healthy but uve had a few local issues with that leaf and maybe a few others, read the leaves and you will yield imo

stringer420 said:

Idk but its on just one leave wanna catch it before it gets worse, im leaning towards nute burn??

Click to expand...

Plant's fan leaf got too close to the light and got burned. That is not a nutrient burn as it would not be present on just one leaf and looks nothing like most nutrient burns. It is also not the color of most nutrient deficiency which form "rust spots" that are indicative of a micro nutrient deficiency. I didnt read what you are using as a light, but it is likely that that leaf was touching a CFL or something similar.

Im not using cfl's and its not close to light at all it was at the bottom of the plant but i do got a light in the middle of the plants also but there a foot maybe 2 away.. so im thinking now thats its from a leaf rest on it