Nutrient burn

Reduce EC of your water and things will get back to normal. Need a bit more resolution than that, but that is the gist.. properly diagnose what is causing it, adjust and it will course correct. Great thing about hydroponics is any change is immediate, but bad thing about hydro is any issue quickly spirals, too. Less forgiveness/rome for error, overall. A leaf chart helps... if there seem to be multiple issues and confusing symptoms, double check you pH ... in fact check you pH first before anythign else as far as that goes with any new problem. Lockout is another prime suspect when a bunch of shit overlaps and you can't easily distinguish what is the actualy cause of the problem beside thinking nearly everything at fault. A good leaf chart is always useful to have. Learn difference between a mobil and immobil nutrient, interveinal chlorosis vs paling from tip - and - in progression etc etc... all will help you delineate what is going wrong. Always easier to ramp up rather than reduce concentration... if unfamiliar, take that safe path and reacting to a slight deficiency is a short-term nothing-burger. push a bit further, see a little burn and dial back... it won't always be the same EC, but it'll be close to it. other relativistic variables are at play, so whatever "optimal" is, it will ebb and flow a bit unless you have lab-precise environment.

Its probably due to the Ec of your nutrient solution being higher then the plant can take.

You have 2 options 1. Do a reservoir change and put in less nutrients. 2. Add PH adjusted water to dilute your current mixture.

What you need to do is a flush. What I do is to prepare another bucket with pH'd water (plain) and transfer the plant to that bucket (make sure you have an air stone going in it). You're going to want to leave it in that 2nd bucket for at least a couple of hours (some say even 24 hours). While that's working, completely clean your original bucket or reservoir. Use H2O2 to fully wipe down/clean it out and then fill it again with pH'd nute solution at 1/2 strength. After a couple of hours in the plain water, you can transfer the plant back to the weakened nute solution and go from there. I looked at both of your hydroponic grows here and you're not giving any indication of the ppm or tds... and this is going to be key as you go forward. For autoflowers, you want the following ppm/EC readings: Week 1 - EC 0.2-0.4 or ppm 100-200 Week 2 - EC 0.4-0.6 or ppm 200-300 Week 3 - EC 0.6-0.8 or ppm 300-400 Week 4 - EC 0.8-1.0 or ppm 400-500 Week 5 - EC 1.0-1.2 or ppm 500-600 Week 6 and the rest of the way - EC 1.2 and ppm 600 Depending on how much damage the nute burn did to the plant, these readings may need to be reduced... if you've fed too much, your plant will show her reaction very quickly - like within an hour or two - so keep checking. If I see an adverse reaction, I remove 1/2-1 gallon of nute solution and add the same amount of clear pH'd water to cut the ppm/EC to see if this helps... and it usually does. I've got 2 DWC grows going, the first one was my "learning" grow and boy did I make mistakes in the very beginning... but my second grow is the beneficiary of all the knowledge I've gained through my mistakes with #1. #1 has been really damaged with all my mistakes and so, at 5 weeks old, she can't tolerate the ppm level that my #2, at 3 weeks old, is able to withstand (same strain, same seedbank)... so I just have to "read" her and give her only what she can tolerate. Good luck!