So after the roots have been wetted and you’ve loosened the plant from the pot, you are going to dump it out. I can see already that the grower had this in a much smaller pot, a 4 inch square pot and since dendrobium like small pots, I can understand why he would do that. But as I said it is tall and to balance it, it was put in the larger pot. Now what you would like to do is loosen the mix gently and look for any disease, dying or rotted roots. Now these all look fine, these here seem a little wet. I am just going to feel them. These seem a little rotted here. If you pull on them you can see those little white strings, the outer coverings coming off. You are left with this string, the inner surface of the root.