I'm more of a 75:25 for alcohol:white vinegar too much acidity can aggravate the external ear tissue but everyone is different so you may want to experiment a bit to be honest and find what's best for you.I agree - However I simply use 50/50 alcohol and vinegar. An ounce of prevention is worth a pound of cure.
I lost a few days diving in Indonesia last April due to irritable and itchy ears and I've changed my ear beer formula a bit which worked great when I returned to Indonesia in October and dived nine days straight with no issues.