We have a cocker spaniel who has only had problems with ear infection before she came to live with us. At 5 months she had only eaten a popular commercial brand of food and always had terribly infected ears.
First thing we did was get her a good ear cleaning at a groomer. On the way home we picked up Colloidal Silver and gave her a 7 day treatment (the bottel calls for 14 days but there was no need in her case). We gave her this treatment orally for 7 days and cleaned her ears religiously.
At the same time we switched her food to a Fresh Raw diet.
She has NEVER had any troubles with her ears since...in the past 3 months I have only cleaned her ears once and only because I wanted to freshen her up...Her ears are clean as a whistle and free of infection.
Hope this helps! Good luck!