reduce feeding ppm to 300 flush plants regularly until the plant shows signs of accelerated growth and if your hydro then dial in ppm ph temp and they should snap back quick, just remember always run newts at 2/3 recommended values and adjust accordingly for the plant and conditions. Look newt burn is good to a point and now you have tested your plants limits but the best is it did not make it to the top of the plant and bottom leaves always show signs first.
even after 20 yrs i run 2/3 values.... good luck...