I'll add an update, i somehow always land here when i research the strain again.
Flower week 5. My fav strain so far. In RDWC it's a light feed at 1 EC at week 5 flower. I went 1.2 and you can see the tip burn.
250 ppm is really low I would bump it up to 400 again. Your PH at 5.5 is low and I would raise it to 5.8 unless you swing that range and PH down to 5.5 again; in that case you are ok.
My guess here is PH issue or you have root rot. Let's see them roots :)