How long can an ear cold last and what's the best treatment for it?

Depends what it is..: An "ear cold" does not have a strict medical definition and i would suspect could represent one of 2 things. One is a true bacterial infection of the middle ear(otitis media) which often can require antibiotics to clear up. Another would be eustachian tube dysfunction in which a cold or allergies can block the drainage tube of the ear and this can last until the cold resolves or longer 1-2 weeks.