Potting media for Dendrobium

[aliceinwl]

I have a Dendrobium Roy Tokunaga and a Dendrobium Little Atro. They're both potted up in a media that seems to predominantly large chunk perlite with a little peat moss or similar material. I bought them back in March and the vendors indicated that they wouldn't need re-potting for awhile. They've been holding pretty much steady with not a lot of new growth. The media they're in drys very quickly so I was watering them every 2-3 days over the summer but have scaled back now that temperatures are cooler.

I'm wondering how these would fair in a bark mix and is there a good time to repot? The Dendrobium nobile and Dendrobium phalaeopsis types I have in bark seem much happier. The Dendrobium moschatum bare root keiki I bought this summer also seems to be establishing quickly in bark with two new canes already forming at the base which is more activity than I've seen from the Dendrobium Roy Tokunaga and Little Atro.