DH often feeds the rabbits before work, when it's still dark. But if he's running late, DH will call me after it's light outside for me to feed them. That's when I noticed one of our rabbits ears looking gross. So I suggested DH go out to check that rabbit in during daytime - he said it was probably ear canker or mites, and mineral oil usually worked.
We didn't have any mineral oil, so I used hydrogen peroxide with Q-Tips while DH held the rabbit. The really bad ear started looking just a teensy bit better after three days using hydrogen peroxide. Then I went grocery shopping and remembered to pick up some mineral oil. It made a huge difference in just one day!
The bad ear had inflammation towards the lower part of the ear, where the canal goes into the head. The peroxide hardly made any difference at all on the inflammation. One day after mineral oil, I couldn't see any inflammation at all!
After day two on mineral oil, DH said the rabbit shook his head as DH put him back in his cage, and a large scab came out the rabbit's ear, leaving behind pink skin. Today is day three on mineral oil, and most of the inner ears are both pink with intact skin, with a spattering of very small scabs.
None of the other rabbits have grungy ears, and the one that had mites/canker was born in captivity. Also, his cage is in between other rabbits, so I have no idea how just that one rabbit got mites in his ears and no other rabbits did. But just to be safe, I think each rabbit should get at least one squirt in each of their ears preventatively, in case mites are in their ears, but just not visible yet.