So today I was looking in my freshwater 15 gallon tank and I noticed that my Corydoras Haraldshultzi otherwise known as Harald Shultz's Cory was looking pale and was breathing very shallowly and had small fin damage and couldn't swim or eat. I was like crap my fish is really sick so I looked it up and some people said it might be columnaris but I wasn't sure. Came back home few hours later and my fish is dead
. I want to know what it is and if the rest of my fish will be okay and if not what I should treat it with. It is too hard to really see what is wrong with him so I don't really want to put a pic in. Also I was thinking of putting some furan 2 in but I am not sure if that would help if my other fish were susceptible of getting it.