Coco chunks will be fine. As in croutons and such ? Thick pieces and squares ?
It's the fine grade coco you don't want. Might fall through.
I use a Rapid Rooter plug for my seeds, then into the net pot.
They are made from coco fiber and don't pose a problem, like with ph and over watering like rockwool.
Basically a big ass coco chunk too ! lol
You can go right into the bucket with the pot too.
Just make sure it fits.
Seen another grower do this on another forum.
6" square pot with coco croutons, into bucket.
Same massive root development.
Actually, you do have to treat those coco chunks and croutons.
Good info on it at breed bay .com ! There's a coco sub-section. READ IT !!