ouch!!

Hey guys anyone know what causes this???

Could be a number of things mate.

What are your specifics?

Soil/Hydro, Nutes, Light, PH, PPM...etc..etc

Just a quick suggestion, could be Soil/Hydro, Nutes, Light, PH, PPM...etc..bit looks like heatburn to me

Quick guess would be spider mites, check the underneath of your leafs with a magnifying glass if you can

Just looks like nute burn to me as far as I can tell from the pic.

Spider mites don't leave that kinda damage, the leaves seem to be contorting and burning up. Toxicity would be my best guess.

It doesn't really matter which nutrient is toxic just flush.