Brooklynella! HELP!

[George]

First you need to make sure it's really brook that you are having, not marine velvet, not marine ich because their symptoms are similar.
If you are sure it's brook, you want to get the clown fish to a QT tank ASAP because all the proven treatments for brook are deadly for invertebrates (i.e. your anemone and crabs). A 5 gallon salt buck is good enough for a clown if you don't have a QT tank set up. Need heater and airstone. Do regular water changes.
Treat brook with either copper or formalin (if you can find it). Treatment protocols should be all over the internet or on the bottle.
Leave the DT fallow (fishless) for 12 weeks.
Good luck.