[BigReepher]

It does appear to be brook, it is highly contagious amongst clownfish. Formalin has been known to work and I've used it successfully. I would probably try to catch any other clowns and give them a dip. Check water parameters and make any changes slowly. The formalin dip should be done as carefully as possible to keep stress to a minimum. Keep in mind that the formalin will reduce oxygen levels as will higher water temps so don't use a dip with a temp over 79. Good luck!