You should a for a pH of 5.8 in coco.
I was thinking along the lines of mixing peat moss with the coco; possibly 50:50. The peat will hold moisture and so it will hold the water soluble nutrients. Using to much peat and the mix might not dry out enough and then root problems can start. I sometimes think of using some vermiculite and reducing the amount of peat moss. @HaremMasterOG covered a lot of what I was thinking would work for the auto-pot system and some of the problems.Thanks for the information. That is interesting. I would likely not use the biochar then. You mentioned you know how you would do it if you were going to try organic nutrients in coco. How would you do it?