Just brought home a big black arowana and it has fin rot that is progressing very quickly. It is already reaching the body in some places. I have the aro in my 480 gallon with some stingrays. I'm hoping to not have to medicate the entire tank, but I will if need be. I just added salt at 1 tablespoon per 5 gallons. I do have some water treatement on hand for bacterial and fungal infections if I need to add it.