Mites are usual cause of crusty ears in cats. If you are sure that there are no mites then other possible cause can be bacterial infection. First of all you wash ears of your cat with per oxide. After this use topical antibiotic cream or antibiotic spray which is more effective than cream. The treatment will respond within 2-3 days.
You can also visit to a vet to avoid further spread of infection.
Do not use hydrogen peroxide to clean your cat's ears--this actually causes tissue damage.
The discharge may be caused by mites, or infection (yeast, bacteria, or both). Your cat needs to be examined by a veterinarian, have an ear cytology done to determine the source of discharge, and start appropriate treatment. Your veterinarian can also give you an appropriate ear cleaner that is safe to use.
Is it a clear crusty or a dirty looking crusty? What your describing sounds more like the clear version, which wouldn't be mights but, more of a weepy skin irritation. Maybe some kind of allergy. It is still best to have your vet verify what kind of issue this is. Good luck.
Sorry I don't have an answer, but my cat seems to have developed something similar. I was wondering if you ever found the cause and, perhaps more importantly, how best to treat the condition?
I suggest you sign up for cats.com.
It has a lot of info about cats.
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My cat has sumilar crusty, clear discharge. My other cat had the same several months ago and the vet didnt know what it was, and had to be put to sleep because the build up was was causing pressure on the brain the vet thought. As the visit to the vet seem a waste of money and had a bad outcome any ideas what to do>
My cat had a yeast infection, was treated and then it came back with a vengence, back to the vet Bubba went, QuadraClear Drops 2x a day for 10 days! He hates it but we have a follow up in 2 more days I am hoping that it is finally clearing up, he's been miserable :(
I wouldn't put anything in or on cats ears unless I am instructed by a vet, in the long run it's worth professional advice!