I am not going to try to research this, because I think Suigeneris, or one of the others is better qualified than I am
I was feeding purina and stopped about a year ago and am now feeding blue buffalo, but they were so bad from the purina it has taken this long to get it out of their system, both had a huge dry patch with almost all the fur off going down their back, now its all grown back and just a small patch of dry skin above the tail, so the new food id doing good, im not spending much on supplements, Im giving olive and fish oil for the omegas and a bottle of vitamins for dogs wasnt much and im crushing up human glucosamine and chrondroiton tablets into their food for joint help..their ears have been good for along time and just once a month ill give a squeeze of the zymox just as a precaution..I use Dawn because I keep it around for fosters, and a little goes along way cutting grease to get water penetrate. I only bathe every couple of months or when they find something dead to lay on, and my youngest is double coated. I'd consider changing food if you are having to spend that much on supplements, what are you feeding? (I use zymox for ears too but not often, like if I see something)
amazon sells it and I have read the precautions for it, I have alot more dangerous chemicals and stuff around than that, but all is handled with extreme care and with all safety precautions for eyes and skin...that high strength peroxide is dangerous, even storing it, it's kind of volatile. You have to dilute a LOT