Defficiency or light burn?

The only things that are making me unsure is her red stems on some unaffected leaves which aren't close to the light, and there being absolutely no other signs of light stress, that I can tell anyway, surely I would have more yellowing before browning? Can a K deficiency show up on upper leaves? I could dim my Mars Hydro TS1000 to 100w down from 150, this OG kush exploded on me there's no more room in the tent to go any higher. I should also add my EC coming from the tap is farely low, and Ive read that mid flower plants require more calcium, so I have added a prevention dose just in case my source water and nutes do not contain enough, My town provides a full drinking water report https://i.imgur.com/QiNG5hd.png

Personally I would say your lights are to strong so I agree with thraxa raise them it happened to me at one stage didn't know what was going on 😂

Since the strain has not been added by the breeder; its a 9 week finishing photo