Canine Candida?

I have a 12 year old neutered male black Labrador Retriever. We adopted him about 7 years ago from the local SPCA. My question has to do with his ears. He has forever flapped his ears sometimes to the point where they would burst and spray blood on the walls and furniture. They are full of black, gooey gunk that has the most disgusting odor imaginable. I have tried cleaning his ears using hydrogen peroxide but nothing is seeming to help him. We have tried changing dog food brands and that hasn't helped. The vet prescribed Otimax to relieve his discomfort but it is very expensive and it only treats the symptom. Thanks for any suggestions.