help me plz. light burn or nut?

Thank you. I added a few photos to my profile in this regard right now in the fourth week. It may have been a physical injury when I was training them. But the leaves on the plant start to turn yellow from the tip. I do not add fertilizer to the water, however, the ppm of the city water is high pH 6.8 ppm 400 500 and Ranf pH 6.2 and ppm 2000. Can someone tell me with what pH to water them so that the ppm of the pots comes down? The lights are at 45 cm