Nutrient Burn, Leaf Septoria, Nutrient Deficiency? Or something else?

Hi! Are you blasting that led at full power all the time? Seedlings and young plants don't need that much power and they can't even handle it that well, so it might be that you have been given too much light for them and they are stressing out. Also 24hrs light can be very stresfull to plants and even so if they are stressed to begin with. Your ec is 1.7 and humidity at 40% so you have been giving quite alot of nutes and your VPD (Temp/Humidity ratio) is way off 'cos they would like to be at 60-70%% in veg state and even 80% when seedling. pH is little bit high for hydro BUT if you are using "bennies" (Beneficial bacteria and mycorhizzae) you can also grow "bioponic" and you can grow with higher pH than normal, but I don't think thats the case rn. Dilute your reservoir to 1.1-1.5 Ec Lower your pH to 5.5-6.0 and keep it there Raise humidity to ATLEAST 55% better yet 70% Change light cycle to ATLEAST 20/4 or better yet 18/6 for a week to ease the stress and give them some rest Raise the light 24" or as high as can if 24" cant be reached With these you should see them grow much healthier and better in after about a week or so