Bro, thats all root rot and algie growth in your res and sidelines of water levels.
Im 1000% positive both of your meters are junk. There is no way that solution is 1600ppm, and if it is, its green lol. . what is it full of algie? Then even though they are not slimy, they look brown and that netpot looks like it can be cleaned with a rag and turned brown. Thats rot my friend. They way they go from brown down to white yea. . .
So anything that isnt under water is brown it looks? So what do you do lol .. idk man, i mean its all fixable. .just gotta study this thread about how to run your system, and make another one on what to add to your pot. Cause atm you have problems with your setup, and everything your adding. Everyone does though, there are few who master it day one lol, but its a challenge in itsself to go hydro, but I assure you its worth it.