2 parts soil, 1 part coco. And now I do what I call the permanent pot. Sorta like no till. I just cut out the stump, and plant in the hole! On my fourth grow doing this and it works well, I've had no issues. I may dump the pots at the end of this grow, bust up the rootball a bit, and a little fresh coco and soil then back in the pot it goes! No need to worry about disposing of medium! And it shows that even using Megacrop for nutrients, there is life in the soil. the roots breakdown quickly. As an experiment, I kept a pot in the base after chopping the plant for a month, then removed the stump. Just pulled it right out, most of the roots had already broken down.
When I cut out the stump, I have an old, serrated kitchen knife I use. I cut a hole slightly smaller size of my starter pot and push the new plant into the hole, slight;y compacting the rootball, like putting a plug in a sink lol!