Problem with dendrobium nobile

[Plant gril]

Hello! Theres been a problem with my dendrobium nobile, I have it since last year and its leaves started turning yellow from the tip, then brown, even the new shoots! They are dry, but I water it like twice a week so not the lack of water is the problem. I have examined its roots, took it out of the pot, seems okay to me. I havent fertilized it with anything yet and there is enough humidity for it. So if somebody could tell me what to do with it I would be thankful