One ear / infections over and over – suggestions?

Hi basset lovers. We have our 2nd Basset Hound, our first full bred one. She’s the best!!! But we have been struggling for the over a year now with one ear. We have been feeding her Purina Pro Plan since we brought her home at 6 weeks old. She’s almost 4 now. Last year, vet put her on hydrolized protein food temporarily and the infections stopped. Then we eased her back to her treats first, then to the pro plan, only salmon or lamb. We were good for months, but now she has another ear infection. Haven’t paid for allergy testing. At this point cleaning her ears every week. But we need to stop the infections. Any suggestions? Anyone’s dog on hydrolized protein food 24 hours.