Nutrient burn or not?

Further to my earlier point, I've just noticed the temperature of your water - you should aim for around 21°C, as water is less able to dissolve oxygen at temperatures as high as 28°C. I doubt that's the cause of the issue at present, but it will cause problems with your roots later on if you do not fix this. I also agree with @Roberts - get some dedicated cannabis nutrients and your plants will thank you for it later.

You don't need to add any nutrients for at least the first week. The seed itself contains all the nutrients the plant needs to get to 2-3 sets of proper leaves. Flush with water and don't give any nutrients until you see two sets of leaves.

Need to know your ppm. It's most likely a little high bro if your ec is that high. Seedlings are easy to burn. For regular photoperiod you want around 200 ppm for seedlings and half that for autos in the first week to avoid burn. Also your water temp is a little high.

With seedlings. Water is best. Then apply nutes with hydro after a few days