Unknown fish disease please help!!!

[fishyfishie]

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.

 

[V227]

If the surviving tankmates aren't displaying symptoms, not a good idea to blindly medicate.
I suggest doing a 50% WC & closely watch for additional casualties. Be prepared to remove any obviously infected fish asap & treat in a hospital tank.