buds not growing

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 :(

Idk what week it is but the buds are not very dense and 1or2 of my plants hairs are almost all brown, I checked for a hermie I don't have one, bit the trichomes are all good and clear, is this just what happens?