We cannot blindly conclude that you have nutrient burn; However; If you do in fact have nutrient burn, then you need to flush the plant with ph’d water, (5.8 for hydro, and 6.5 for soil), 3 times the capacity of the vessel you are using.
i.e.
3 gallons for 1 gallon pot.
9 gallons for 3 gallon pot
18l for 6l pot
Hydro. Just fill a 5 gallon bucket and flush the medium until you have a low ppm, near your source water’s ppm.