My black lab had ear infection issues for the longest time and we treated him with everything under the sun the vet could think of, she ran every test. I changed his food, made his food, and finally the one couple things that have helped are warm water mixed with apple cider vinegar to clean the ear if its full of debris. Then after the debris is cleaned I put a few drops of tea tree mixed with coconut oil.
I do this twice a day until I see improvement. Its important to clean the ear thoroughly by massaging under the ear drum while the vinegar water mixture is in the canal. Let the dog shake his/her ear after you put the fluid in it will loosen and debris and then take either a cotton ball or gauze pad to clean completely.