I can't really tell much from that small gif. Can you please describe symptoms (see below for Brooklynella)? Also, how long have you had this clownfish?
Brooklynella:
Symptoms – This is most often seen in clownfish, but it can afflict any fish. The fish’s skin will appear to be peeling or sloughing off, oftentimes causing excessive white mucous to form around the affected area(s).
Treatment options - Formalin bath, followed by additional formalin baths (as needed - but give the fish a day to recuperate in-between baths). You can use formalin in a QT (at a much lower concentration than the bath), but great care must be taken to provide plenty of gas exchange as formalin will quickly deplete the water of oxygen. For this reason, doing baths is the safer option as the fish can be pulled from the formalin if showing signs of distress. Formalin-MS is preferred, as that contains 37% formaldehyde. However, in a bind, any medication containing formalin (ex. Quick Cure) is better than nothing. Alternative treatments for brook include metronidazole (ex. Seachem MetroPlex) and acriflavine (ex. Acriflavine-MS). A freshwater dip may provide temporary relief if you are unable to locate any of the aforementioned medications right away.
