I am growing in a 12x12x8 sealed separate building. I am growing in pro-mix hd remixed 3:1 with perlite. I am feeding the complete GH line in the drain to waste schedule.my plants did well in a feed only schedule until the second week of flower. At week 3 of flower I got tip burns on some of my top leaves. I tested the runoff with meter and got over 2000ppm. I since have run just an r/o water flush with a runoff test of 1800ppm then a half feed and the runoff tested at 1600ppm. My question is should I run an r/o only flush again and then return to feed feed water? I am lost.