How often is your a/c running? Your a/c will cause the humidity level in the room to drop, combined with the close 1000w could be causing some burn issues. Really need to get a hygrometer of some sort, you want your humidity in flowering around 40-50%.

Are your other strains as tall as this one? Is it only the top colas on the plant that are affected?

Is it hot to you at the top of the canopy?