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Could be scale. Could be biofilm.You can use a product such as Swirl Away or spa Purge, which are "pipe cleaners". You could ignore. Most people do.
The clear hose always looks great when new until it gets a film and gets that "milky" look. You could try to get it off but A) it'll come back, B) you may know it's there but no one will see it.Ignore it, close the panel and enjoy the spa and just worry about routine water maintenance.
If it won't hurt thub, then that is what i will do... Thanks
The tub should be fiine. Leave it alone.