Ok so 1st it ain't Hydro , it's coco growing with automatic irrigation , it's not the same , it's similar but not the same as you can't over water in hydro but it's possible in coco and there are more little differences like that.
That said there is a similarity in hydro and coco : you are feeding straight from day one and the week 2 EC can be around 1.2/1.4 with healthy plant , so you need to feed and the dosage is significantly higher than in soil growing , what I can see is that you are not telling us which ec/ppm level you are running so it could be too low ans the plant is running out of nuts( not too high or the symptoms would have been differents )
The ph is wrong , correct it to 5.8 the sweet spot in coco and stick to 5.8 , measure the water runoff PH too to know how much the variation of ph between the input and the output is high and correct the input according to the output : ex 5.6 output then water with 6 ph to get back to 5.8ph quickly