@Leafy it might not be a ph issue do you use nutrients if so you could have to high of an ec or ppm , when I first started growing in Coco I feed every third day and everything grew well until about the 3rd week of bloom then that was it they stopped well I found that the nutrients didnt get washed out and there level just went up and up I had a ppm of 5000 and it was supposed to be about 1000 a little high well it took forever to get all the nutrients out but once I did the plants flourished , Know I know you are using compost is it possible that you got a really hot bucket of compost or a really weak one