Anybody know why I’m seeing brown spots and burn...

This looks like a nutrient lockout but as mentioned by our friend @DudeGrowsWeed your EC/PPM looks fine, so I'm thinking that your TDS meter may be dysfunctional. If the yellowing tends to spread in the next days, I'd recommend to flush your system with plain pH'ed water for a couple of days until the new healthy leaves appear. I'll be around, good luck with these beauties!

Ok well i am no expert and never done hydro before other then testing the Kratky method which did work for cannabis. However i do love researching and reading all things cannabis every day. If it hasn't been changed in awhile just do it get it over with unless you don't have too. Tips and browning i noticed this on my grow doing week 5-6 also if you haven't added any nutes i am going to say check the PH. If the PH is fine look into the nutrients as i am thinking they may be calcium and/or potassium deficient. Good luck.

Hey there happy 4:20 to you too! Your plants look nice, especially that last photo. I'm not any sort of expert or anything, but with a hydroponic system are you able to check out your roots and make sure there's no rot happening? I expect you could most likely smell it, but I know good root health, clean properly ph'd water are the most crucial elements right? Maybe flushing the water like you mentioned wouldn't be a bad idea. I'm so sorry you can't maneuver around your setup, its so hard to properly plan out the space and how much room you'll have once they get big. I hope you can manage to get your good defoliation done. 🌎 happy 4:20