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.
This is just my opinion. First, those plants don't look bad. Tip burn isn't too bad in my experience. I personally wouldn't flush for that but I see why you did, high ppm run off. I would say just lower your ppm next feeding if you're worried. Are you using the GH recommended nutrient strength and schedule or adding nutrients based on ppm reading?

I use GH gro, micro, bloom. I highly recommend using their feeding guidelines and not adding nutes based on ppm meter reading. Let me say i messed up big time basing my nutrient strength on my ppm meter reading. I kept adding nutrients because the ppm meter kept reading low so i ended up adding double the recommended GH strength/measurment and burnt the fuck out of my plants. Like leaves crispy and falling off.

See what other people think. I'm new to growing cannabis so I'm no expert on the topic.