I would use 10% citric acid and 5% sodium chlorite. The idea is to form chlorous acid and introduce it to the ear canal. The mixture has free chlorine dioxide as well as a measure of available chlorine dioxide. As the solution sits in the ear the free chlorine dioxide attacks the infection. As the free chlorine dioxide gets used up the chlorous acid makes available more chlorine dioxide from the available chlorine dioxide in the solution. Using HCL doesn't work as well as using citric acid .
In the drinking water you are going for a target of 5 PPM available chlorine dioxide. Using 0.3% sodium chlorite you would use 0.83 ml of the 0.3% in 500 ml of water.