The preliminary judgment is that the fin is infected with water mold or bacteria after being scratched at the opening of the culture box. If left unchecked, it will rot and eventually lead to fin fracture.

Treatment: Take out the sick fish, scrape off the sarcoma with your nails, pay attention to scraping it clean, and then suck up the water on the fin with a napkin. Apply the medicine directly to the wound, let it absorb for a while, then keep it in a fish tank for three days, and it will be fine on the third day.