There are black things on the cat's ears
Black spots on a cat's ears are most likely caused by ear mites. In this case, the owner can use ear cleaning solution with anti-mite and antibacterial properties to clean the ear canal and isolate the infected cat for treatment. In addition, the owner needs to maintain good hygiene, and it's best to disinfect the cat's belongings with disinfectant and a UV lamp. 
If your cat has black discharge on its ears, it's very likely due to an ear mite infection. The black discharge is the excrement secreted by the ear mites. In this case, you can use a cotton swab dipped in saline solution or baby oil to gently clean the discharge.
2. Ear dropsEar mites in cats reproduce rapidly and live deep in the ear canal, making them difficult to eradicate completely and requiring manual intervention. In this case, owners can use an ear cleaning solution with mite-removing and antibacterial properties to clean the cat's ears, thus achieving a complete cure for ear mites.
3. Isolation treatmentEar mites in cats are contagious. Although they are not transmitted to humans, they can be transmitted to other cats. Therefore, cats with ear mites need to be isolated and treated separately. After the ear mites have been completely eliminated, they should be observed for 3-5 days to ensure that the cat has no adverse reactions before being kept with other cats.
4. Cleanliness and hygieneCats often develop ear mites due to living in dark, damp, and unsanitary environments for extended periods. Therefore, if you discover your cat has ear mites, you should immediately disinfect the pet items your cat uses with disinfectant, then ventilate the room by opening windows. You can also use a UV lamp to sterilize the area.