plant hospital

Hi all so I’ve been having a problem with one of my plants for a couple weeks now and it’s not growing!!! Just put some pure Ph’d water through my run off ppm was 890 and ph 6.40. I’m in coco by the way. Need some help :(

So i'm having a reoccurring problem with my plants roots. The roots start out very healthy. Plump, nice and white with little white hairs sticking out. But after a few days, the start to get extremely skinny, dry out and get crispy until they eventually just break off. I am pretty confident it...