You should be starting in the pot it finishes in. Those root plug are no good for soil and coco. I have seen them stunt when used in both mediums. They are what i use for deep water culture. You should start with a 400-500 range for coco. The ph of 5.8 is good for coco, you might want to go a little lower. Coco ph buffers to 6.8, so maybe 5.5 to be exact. I start with a 700, but my tap water is a 440 or something insane.