These are the treatment options for each disease I've mentioned. Please read them and the symptoms of each so you can look at your fish and make a decision on which one it probably is. Since you can see your fish better than we can and can see their behavior, your the best to decide at this point.
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.
Velvet (Amyloodinium):
Symptoms - Because velvet can be such a fast killer, key behavioral symptoms will often prelude visible ones. A fish with velvet may breathe heavy, seek relief by swimming into the flow of a powerhead and act reclusive (velvet makes them sensitive to light).
If visible symptoms do manifest; velvet appears the same as ich, except the fish will usually be covered in “dust.” This dust may look gold colored if viewed at the right angle and under the right spectrum of light. Velvet is often misdiagnosed as ich and is the main “tank killer” in our hobby. It can wipe out all your fish in less than 72 hours and cannot usually be “managed” as ich sometimes is.
Treatment options - Chloroquine phosphate is the treatment of choice for velvet, but copper also works if symptoms are caught early on. Tank transfer and hypo does notwork with velvet. A freshwater dip or formalin bath is recommended before treatment begins, due to the severity of this disease; however these would only provide temporary relief and will not eradicate velvet.