I have one 25' cannula extension hose on my concentrator which extends out to my recliner for TV viewing. I use a 7' cannula hose on it which I change out every two or three weeks depending on how stiff the ear tubes get. But I have not changed the 25' extension since I put it on about two months ago. I do not use a vaporizer on the concentrator but I now realize that mold could be forming in that long hose. It is hidden behind the bed headboard and night stands so is difficult to see. Any recommendations on how often it should be changed? I do not see any liquids in the 7' cannula hoses.