I agree with Drstrangelove, columnarus will remain after the infected fish is removed, and is very hard to get rid of. It can exist in a suspended state in damp mud for years (even frozen mud), and will rest in the gunk in filters, in substrate or wherever there is detritus, and can suddenly reappear.
I was given some Mayaheros beanii that were infected, after they died, i treated the quarantine tank with Hydrogen Peroxide a number of times to sanitize it.
If it hit one of my tanks again, I'd tear it all down, bleach everything in contact with the tank, and let all that stuff sit totally dry for months. And probably bleach it all again, before re-start-up.
I know this seems drastic, but its what I'd do.
And as an aside, columnar becomes most virulent at water temps above 82'F, so unless the fish was a species like Nandopsis haitiensus, Alcolapia alcalicus, discus, or some other hot water species, I'd never use temps at or above 82'F again.
The infection has very differing symptoms depending upon severity, and water temp.
Below is one of the beanii, with acute columnaris