First Grow, auto flowering

**This happened at the end of the week, photos will be in next week diary but know that the quick one is loosing many leaves, they are burning and curling, brown and copper 😭 After 6 mostly flawless weeks i'm facing the first real problem in my growth, not sure what it is (maybe calcium deficiency) but I think I know what is the cause of this problem,. For all this time I'be been trying to water the right amount and I thought the right amount was to not have ANY runoff, never.... well... salt build-up is a thing... and after testing runoff with a water at 6.7pH and 240ppm, the result are clear : pH 6.0, ppm 1800 😟 I flushed them all, I'm not sure the quick one can make it, i'm 5 days ahead this journal and she is still getting worse but the others seems to be ok and the northern light is less yellow, from now on i'll water with 10-20% runoff every other time with clear water and see how it works. I'm learning the hard way but still happy as my next plants will be happier