If your clown had Brooklynella, then ALL of your fish have Brook even if they don't exhibit symptoms and so does the tank. The parasite for Brook, unlike the one for Ich, multiplies by cell division. The new cell becomes a "swimmer" looking for a host. If it does not find one it dies. Swimmers can persist up to 4 weeks so you tank has to remain fallow (fish-less) for 4 weeks. The only thing that will cure Brook is Formalin 37%. This should be available from your local aquarium shop. You need to administer 5 Formalin baths. You put 1 cc or 20 drops of 37% Formalin in one gallon of water. Make sure the water is the same temperature and PH as the tank the fish comes out of. You put your fish in the bath for 45 minutes making sure to monitor it just in case it shows signs of extreme distress. Do this every other day until you have given the fish 5 baths. Make sure the fish is NOT returned to the main tank until it is fish-less for 4 weeks. If you return it to soon, it will be reinfected with Brook. Having said all this, are you sure your fish does not have one of the various forms of Ich? Because of they have Ich, Formalin will NOT cure them. For Ich you need to put them in a copper tank for 4 weeks and the main tank would have to remain fallow for 8 weeks. The reason being, Ich's life cycle includes eggs which can remain dormant in the substrata of your tank for up to 8 weeks. When they hatch they MUST find a fish host or they will die. Since both Brook and Ich have much the same symptoms, most of us treat them for BOTH when they exhibit symptoms such as, not eating, lethargic, spots (but not always), slime from the mouth or gills (looks like a clear white coating), damaged fins, loss of color first around the head then the whole body, lesions (but not always). Any significant change in behavior. As for the white spots, this is the parasite embedded in the fish. A fresh water dip of 15 minutes should see a reduction in the spots and give your fish some relief but THIS IS NOT A CURE.
